Absence validation formula behaving weirdly

Summary:

We have created an absence validation formula, for sandwich leave cases.

For example if employee has applied a leave for 9 Jan , they should not be allowed to apply a leave for 12 January.

From employee's ID, when we apply for 12 Jan , it throws error however when employee tries to click on OK and repeats to apply multiple times , the system allows to apply.

If anyone has faced this issue, please let us know.

Content (please ensure you mask any confidential information):

Version (include the version you are using, if applicable): 25C

Code Snippet (add any code snippets that support your topic, if applicable):