Bug: Negative line for serialized item not creating new serial number in debitor system

[logicguy1]

Description

When creating a negative line for a serialized item in the debitor system, the system should automatically create a new serial number in the serialnumbers table. This functionality is critical for tracking equipment that gets swapped and resold to other customers.

Currently, the system is allowing users to select an existing serial number for the second line, which breaks the intended workflow.

Expected Behavior

• Creating a negative line for a serialized item should automatically generate a new serial number
• The new serial number should be added to the serialnumbers table
• This enables proper tracking when equipment is swapped and resold to different customers

Current Behavior

• The system allows selection of existing serial numbers for negative lines
• No new serial number is automatically created
• This prevents proper tracking of resold equipment

Steps to Reproduce

1. Create a negative line for a serialized item in the debitor system
2. Observe that the system allows selecting an existing serial number instead of creating a new one

Visual Evidence

The screenshot shows that users can select a serial number for the second line, which should not be possible.

Impact

• High Priority: This affects equipment tracking and inventory management
• Breaks the resale workflow for swapped equipment
• Prevents accurate serial number tracking across customers

Additional Context

This functionality worked correctly in the past but has regressed. The system previously would automatically create new serial numbers for negative lines without user intervention.