Created attachment 204119 [details]
Outline 2 style in the original document and in the saved PPTX

This is related to bug 169548 and bug 169524

In Impress, there are paragraph styles supported, but not in PP.
As can be seen with attachment 204073 [details] from bug 169524 and its twice saved as PPTX version attachment 204108 [details] from bug 169548, some of their settings are applied incorrectly.

The default "Outline n" paragraph styles have a bit of default Above paragraph spacing set, 0.50 cm for Outline 1 and 0.40 cm for Outline 2, which styles are used in  attachment 204073 [details].
In this case, these are overridden by 0.6 cm Below paragraph spacing for Outline 1 and 0.2 cm Below paragraph spacing for Outline 2.

Upon export to PPTX, these can not be represented correctly as para styles, so they are not converted to anything sensible and are lost. This can be seen in attachment 204074 [details] from bug 169524 and in the above attached screenshot.

However... upon reopening the saved PPTX, the default Above paragraph spacing values are "seen" for the Outline 1-2 styles, but not yet applied.

Then upon saving the PPTX for a second time, some information is lost - I'm not sure what exactly: there is no difference in PP between the first and second (attachment 204108 [details]) saved PPTX files.

But after reload, these values from Outline 1-2 are now applied to the paragraphs (Outline 1 to not bulleted ones and bullet level 1s, Outline 2 to bullet level 2s), so they have more spacing above than in the original file.

After save to PPTX the third time, these values are actually written and visible in PP as well.

Version: 26.2.0.0.alpha0+ (X86_64) / LibreOffice Community
Build ID: c8fa51cec19eb89ef1506adfd461e5fdbcb4477a
CPU threads: 32; OS: Linux 6.14; UI render: default; VCL: gtk3
Locale: hu-HU (hu_HU.UTF-8); UI: hu-HU
Calc: threaded

Unlikely that this was ever working correctly, but there are many steps, any can be considered "broken" by a given commit or another.