Invoice Validates Without filling the Mandatory DFF

Summary:

've configured a Descriptive Flexfield (DFF) on the AP Invoice Header , and made it conditionally mandatory using an EL expression with Page Composer in a Sandbox. The DFF is placed under the Additional Information tab, and the UI correctly displays the field with a asterisk when the condition is met.

However, I've encountered a puzzling behavior:
• If the user does not visit the Additional Information tab, they can validate the invoice without entering a value in the DFF—even though it's marked mandatory.

• If the user does visit the tab, the validation fails as expected when the DFF is blank.