Aha!
Now I found out what actually happens (unless its still more complicated):
when copy-pasting filters from clip to clip, and when the source of copying has been analysed, that status is copied along the filters (at least to when pasted to part of same source clip). And no analysis for the other parts of the same source clip is triggered, and export is happily run without analysis and without warning.
This also explains why the stabilization seems poor sometimes… no actual stabilization happened as material was not really analysed despite filter settings screen saying so.
So whether filter is added “individually” to the clip or copy-pasted (along with color grading etc) the results are different.
For this biggest one analysis was never run but still says “Analysis complete”. Just coypasted the filter settings from the smallest. Asking to export also does not trigger analysis.
In what situation it should ask for a name for the stab file?