I generate PDF files, and I have noticed this limitation. The loss of information on export/import seemed to confirm it.
From my understanding of PDFs specs it requires B painting operator. Otherwise S operators are used for stroke and F are used for fill. My suspicion is that B operator falls back to stroke and fill as separated objects. But it might also probably mean that, as you said, objects are saved as S and F instead of single B operation too.
I generate PDF files, and I have noticed this limitation. The loss of information on export/import seemed to confirm it.
From my understanding of PDFs specs it requires B painting operator. Otherwise S operators are used for stroke and F are used for fill. My suspicion is that B operator falls back to stroke and fill as separated objects. But it might also probably mean that, as you said, objects are saved as S and F instead of single B operation too.