Description:
When saving a presentation file created with Impress with LO24.8 that contains some math formula editor objects in pptx format, all such objects totally disappear from slides. This did not happen with 24.2
NOTICE that if you open the converted pptx file with PowerPoint, the formula is there; but if you open it again with LO24.8, there is no trace of it

Steps to Reproduce:
1.Create an Impress file, insert any equation editor math formula
2.Save the file in pptx format, and close it
3.Now reopen it with LO; the formula is not there anymore

Actual Results:
the pptx converted file when reopened with LO24.8 does not show all math formulas that were inserted. Not even as transparent objects: they are simply not present anymore.

Expected Results:
Math formulas should be in the file, visible and editable.
Indeed, if you open the converted file with the Microsoft program, formulas are there. So it looks like LO24.8 just overlooks their presence in the file.
However, if you save the pptx again back into odp format, they are definitely lost and cannot be recovered.
None of this happened in LO24.2


Reproducible: Always


User Profile Reset: No

Additional Info:
Version: 24.8.2.1 (X86_64) / LibreOffice Community
Build ID: 0f794b6e29741098670a3b95d60478a65d05ef13
CPU threads: 8; OS: Windows 10 X86_64 (10.0 build 17763); UI render: Skia/Vulkan; VCL: win
Locale: it-IT (it_IT); UI: it-IT
Calc: threaded