[BUG] Head command doesn't take effect

[qianheng-aws]

What is the bug?
PPL query:

source=employees | eval a = rand() | sort a | fields id | head 5

returns rows more than 5.

How can one reproduce the bug?
Steps to reproduce the behavior:

1. Put documents more than the head limiation

POST localhost:9200/{{index}}/_bulk
{"index":{"_id":"1"}}
{"id":1,"name":"Dev","reportsTo":"Eliot"}
{"index":{"_id":"2"}}
{"id":2,"name":"Eliot","reportsTo":"Ron"}
{"index":{"_id":"3"}}
{"id":3,"name":"Ron","reportsTo":"Andrew"}
{"index":{"_id":"4"}}
{"id":4,"name":"Andrew","reportsTo":null}
{"index":{"_id":"5"}}
{"id":5,"name":"Asya","reportsTo":"Ron"}
{"index":{"_id":"6"}}
{"id":6,"name":"Dan","reportsTo":"Andrew"}

2. Query using above query

source=employees | eval a = rand() | sort a | fields id | head 5

It return all 6 rows.

What is the expected behavior?
Should return 5 rows.

What is your host/environment?

• OS: MacOs
• Version 3.5.0-SNAPSHOT
• Plugins

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Do you have any additional context?
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