Internal player Subs issue with remux

all my blu-rays i got i remux(main movie+audio+subs) them so they take less space on my drives.
but when using the internal player i noticed is has issues with the subs,
they vanisch or show up only for a ms.
when using mkv's there's no issue and plays fine.
is this a known issue or does the internal player don't have support for original blu-ray subs and only external subs.