Description:
In LibreOffice 25.2.5.2, when defining a page style with top and bottom margins set to 10 mm and left and right margins to 20 mm, adding a Footer causes the bottom margin to revert to the default value (20 mm). After reopening the page style settings and manually resetting the bottom margin to 10 mm, the value is accepted and the layout is correct. This behavior can confuse users and interferes with precise page layout setup.

Steps to Reproduce:
1. Open LibreOffice Writer 25.2.5.2.
2. Create or edit a page style (e.g., "Portrait") with the following margins:
   - Top: 10 mm
   - Bottom: 10 mm
   - Left: 20 mm
   - Right: 20 mm
3. Add a Footer to the page style.
4. Observe that the bottom margin is reset to 20 mm (default).
5. Open the Page Style settings again and set the bottom margin back to 10 mm.
6. Observe that the value is now accepted and layout is correct.


Actual Results:
Adding a Footer automatically resets the bottom margin to the default value (20 mm).

Expected Results:
The bottom margin should remain at the user-defined value (10 mm) when adding a Footer.


Reproducible: Always


User Profile Reset: No

Additional Info:
- Observed in LibreOffice 25.2.5.2 (system DEB) on Linux Mint 21.2 Cinnamon 64-bit.
- Top and side margins remain correct; the issue only affects bottom margin when Footer is added.
- Minimal test document can be provided upon request.