If the user's entitlement includes public holidays, the ones that fall under their work pattern will be deducted even if they are on maternity or paternity leave.
If you do not want these to be deducted, there are two options.
To manually amend the duration of the public holiday:
Go into the user's planner and click on the specific public holiday date.
Change the duration to 0.
To set the entitlement to not include public holidays:
Go into the user's planner and click the blue Settings button.
Untick Entitlement Includes Public Holiday box.
📌Note: If you do untick this, it will stop all public holidays from being deducted.