diff --git a/src/EFCore.Design/Design/Internal/DbContextOperations.cs b/src/EFCore.Design/Design/Internal/DbContextOperations.cs
index 3daa71f0220..4fab5251b87 100644
--- a/src/EFCore.Design/Design/Internal/DbContextOperations.cs
+++ b/src/EFCore.Design/Design/Internal/DbContextOperations.cs
@@ -336,7 +336,10 @@ private IReadOnlyList<string> PrecompileQueries(
         
         try
         {
-            workspace = MSBuildWorkspace.Create();
+            // Set _EFGenerationStage to a non-empty value so that the design-time build performed by
+            // OpenProjectAsync below doesn't re-trigger the EF file generation targets. Otherwise the
+            // generation targets would invoke this operation again, resulting in a fork bomb.
+            workspace = MSBuildWorkspace.Create(new Dictionary<string, string> { ["_EFGenerationStage"] = "build" });
             workspace.LoadMetadataForReferencedProjects = true;
 #pragma warning disable CS0612 // Obsolete
 #pragma warning disable CS0618 // Obsolete
diff --git a/src/EFCore.Tasks/buildTransitive/Microsoft.EntityFrameworkCore.Tasks.targets b/src/EFCore.Tasks/buildTransitive/Microsoft.EntityFrameworkCore.Tasks.targets
index 8989c09df04..15f0b4d2804 100644
--- a/src/EFCore.Tasks/buildTransitive/Microsoft.EntityFrameworkCore.Tasks.targets
+++ b/src/EFCore.Tasks/buildTransitive/Microsoft.EntityFrameworkCore.Tasks.targets
@@ -173,7 +173,7 @@ For Publish:
        This target has the same Inputs and Outputs as CoreCompile to run only if CoreCompile isn't going to be skipped -->
   <Target Name="_EFPrepareForCompile"
           DependsOnTargets="_EFProcessGeneratedFiles"
-          Condition="'$(_EFGenerationStage)'==''"
+          Condition="'$(_EFGenerationStage)'=='' And '$(DesignTimeBuild)' != 'True'"
           Inputs="$(MSBuildAllProjects);
                   @(Compile);
                   @(_CoreCompileResourceInputs);
diff --git a/src/EFCore/ChangeTracking/Internal/InternalEntryBase.cs b/src/EFCore/ChangeTracking/Internal/InternalEntryBase.cs
index 472b9394662..14ea31cf96d 100644
--- a/src/EFCore/ChangeTracking/Internal/InternalEntryBase.cs
+++ b/src/EFCore/ChangeTracking/Internal/InternalEntryBase.cs
@@ -637,9 +637,19 @@ public void SetPropertyModified(
 
         if (recurse)
         {
+            var newElementState = isModified ? EntityState.Modified : EntityState.Unchanged;
             foreach (var complexEntry in GetFlattenedComplexEntries())
             {
-                complexEntry.SetEntityState(isModified ? EntityState.Modified : EntityState.Unchanged, modifyProperties: true);
+                // Added elements represent pending additions with no original ordinal, so forcing them to
+                // Modified/Unchanged is incorrect and would fail the original ordinal validation. Leave their
+                // state (computed by change detection) untouched, mirroring the bulk state-change logic in
+                // InternalComplexCollectionEntry.SetState.
+                if (complexEntry.EntityState is EntityState.Added)
+                {
+                    continue;
+                }
+
+                complexEntry.SetEntityState(newElementState, modifyProperties: true);
             }
         }
     }
diff --git a/test/EFCore.Relational.Specification.Tests/Update/ComplexCollectionJsonUpdateTestBase.cs b/test/EFCore.Relational.Specification.Tests/Update/ComplexCollectionJsonUpdateTestBase.cs
index 9f2fe402946..6f8bcc48ec4 100644
--- a/test/EFCore.Relational.Specification.Tests/Update/ComplexCollectionJsonUpdateTestBase.cs
+++ b/test/EFCore.Relational.Specification.Tests/Update/ComplexCollectionJsonUpdateTestBase.cs
@@ -592,6 +592,55 @@ public virtual Task Replace_complex_property_mapped_to_json()
                 }
             });
 
+    [Fact]
+    public virtual Task Grow_nested_sub_collection_in_complex_property_mapped_to_json()
+        => TestHelpers.ExecuteWithStrategyInTransactionAsync(
+            CreateContext,
+            UseTransaction,
+            async context =>
+            {
+                var widget = await context.Set<WidgetWithDeepJson>().OrderBy(w => w.Id).FirstAsync();
+
+                // Replace the entire JSON-mapped complex property with a structure where one nested
+                // sub-collection (Inner) has grown from one element to two. The sibling sub-collection
+                // (Others) being present in the type definition is required to trigger the regression.
+                widget.Deep = new DeepData
+                {
+                    Mid = new MiddleData
+                    {
+                        Items =
+                        [
+                            new DeepItem
+                            {
+                                Title = "Item1",
+                                Inner =
+                                [
+                                    new InnerEntry { Value = "inner-0" },
+                                    new InnerEntry { Value = "inner-1" }
+                                ],
+                                Others = []
+                            }
+                        ]
+                    }
+                };
+
+                ClearLog();
+                await context.SaveChangesAsync();
+            },
+            async context =>
+            {
+                using (SuspendRecordingEvents())
+                {
+                    var widget = await context.Set<WidgetWithDeepJson>().OrderBy(w => w.Id).FirstAsync();
+                    var item = Assert.Single(widget.Deep.Mid.Items);
+                    Assert.Equal("Item1", item.Title);
+                    Assert.Equal(2, item.Inner.Count);
+                    Assert.Equal("inner-0", item.Inner[0].Value);
+                    Assert.Equal("inner-1", item.Inner[1].Value);
+                    Assert.Empty(item.Others);
+                }
+            });
+
     protected virtual void UseTransaction(DatabaseFacade facade, IDbContextTransaction transaction)
         => facade.UseTransaction(transaction.GetDbTransaction());
 
@@ -607,6 +656,7 @@ protected virtual IDisposable SuspendRecordingEvents()
     protected class ComplexCollectionJsonContext(DbContextOptions options) : DbContext(options)
     {
         public DbSet<CompanyWithComplexCollections> Companies { get; set; } = null!;
+        public DbSet<WidgetWithDeepJson> Widgets { get; set; } = null!;
     }
 
     protected class CompanyWithComplexCollections
@@ -645,6 +695,34 @@ protected class Department
         public decimal Budget { get; set; }
     }
 
+    protected class WidgetWithDeepJson
+    {
+        public int Id { get; set; }
+        public required DeepData Deep { get; set; }
+    }
+
+    protected class DeepData
+    {
+        public required MiddleData Mid { get; set; }
+    }
+
+    protected class MiddleData
+    {
+        public List<DeepItem> Items { get; set; } = [];
+    }
+
+    protected class DeepItem
+    {
+        public required string Title { get; set; }
+        public List<InnerEntry> Inner { get; set; } = [];
+        public List<InnerEntry> Others { get; set; } = [];
+    }
+
+    protected class InnerEntry
+    {
+        public required string Value { get; set; }
+    }
+
     public abstract class ComplexCollectionJsonUpdateFixtureBase : SharedStoreFixtureBase<DbContext>
     {
         protected override string StoreName
@@ -660,7 +738,8 @@ protected override Type ContextType
             => typeof(ComplexCollectionJsonContext);
 
         protected override void OnModelCreating(ModelBuilder modelBuilder, DbContext context)
-            => modelBuilder.Entity<CompanyWithComplexCollections>(b =>
+        {
+            modelBuilder.Entity<CompanyWithComplexCollections>(b =>
             {
                 b.Property(x => x.Id).ValueGeneratedNever();
 
@@ -686,6 +765,26 @@ protected override void OnModelCreating(ModelBuilder modelBuilder, DbContext con
                     });
             });
 
+            modelBuilder.Entity<WidgetWithDeepJson>(b =>
+            {
+                b.Property(x => x.Id).ValueGeneratedNever();
+
+                b.ComplexProperty(
+                    x => x.Deep, db =>
+                    {
+                        db.ToJson();
+                        db.ComplexProperty(
+                            d => d.Mid, mb =>
+                                mb.ComplexCollection(
+                                    m => m.Items, ib =>
+                                    {
+                                        ib.ComplexCollection(i => i.Inner);
+                                        ib.ComplexCollection(i => i.Others);
+                                    }));
+                    });
+            });
+        }
+
         protected override Task SeedAsync(DbContext context)
         {
             var company = new CompanyWithComplexCollections
@@ -716,6 +815,28 @@ protected override Task SeedAsync(DbContext context)
             };
 
             context.Add(company);
+
+            var widget = new WidgetWithDeepJson
+            {
+                Id = 1,
+                Deep = new DeepData
+                {
+                    Mid = new MiddleData
+                    {
+                        Items =
+                        [
+                            new DeepItem
+                            {
+                                Title = "Item1",
+                                Inner = [new InnerEntry { Value = "inner-0" }],
+                                Others = []
+                            }
+                        ]
+                    }
+                }
+            };
+
+            context.Add(widget);
             return context.SaveChangesAsync();
         }
     }
diff --git a/test/EFCore.Sqlite.FunctionalTests/Update/ComplexCollectionJsonUpdateSqliteTest.cs b/test/EFCore.Sqlite.FunctionalTests/Update/ComplexCollectionJsonUpdateSqliteTest.cs
index 0c4bcd5f64f..7d524fb0fa7 100644
--- a/test/EFCore.Sqlite.FunctionalTests/Update/ComplexCollectionJsonUpdateSqliteTest.cs
+++ b/test/EFCore.Sqlite.FunctionalTests/Update/ComplexCollectionJsonUpdateSqliteTest.cs
@@ -290,6 +290,21 @@ public override async Task Replace_complex_property_mapped_to_json()
 """);
     }
 
+    public override async Task Grow_nested_sub_collection_in_complex_property_mapped_to_json()
+    {
+        await base.Grow_nested_sub_collection_in_complex_property_mapped_to_json();
+
+        AssertSql(
+            """
+@p0='{"Mid":{"Items":[{"Title":"Item1","Inner":[{"Value":"inner-0"},{"Value":"inner-1"}],"Others":[]}]}}' (Nullable = false) (Size = 99)
+@p1='1'
+
+UPDATE "Widgets" SET "Deep" = @p0
+WHERE "Id" = @p1
+RETURNING 1;
+""");
+    }
+
     public class ComplexCollectionJsonUpdateSqliteFixture : ComplexCollectionJsonUpdateFixtureBase
     {
         protected override ITestStoreFactory TestStoreFactory