Negative Balance Validation not working as expected

Summary:

Negative Balance Validation not working as expected

Content (please ensure you mask any confidential information):

Hi,

We have a Vacation absence type where its not allowed to apply for leave if Plan balance is negative.

But Employee is allowed to submit leave request even if balance is negative. Below is the configuration.

Plan Level:-
Allow negative balance (Not Enabled)

Type Level:-

Insufficient balance enforcement (Enabled for Employee , Line Manager & Admin)
Deferred processing on initial entry (Not Enabled)
Deferred processing on subsequent absences (Not Enabled)

No validation FF is attached at type level.

What could be the issue?

Thanks,

JD