subtitle problem in 1080p

[oriels]

hi when im trying to run 1080p (any vid) it run perfectly.
the problem start when im trying to set a subtitle..
i open subtitle and the the movie work fine but every subtitle the move flicker for the time of the subtitle.. that happen just in full size screen mode. but when im in a window mode it work fine.
ok let me explain again:
im open a movie.
ok all fine
next im enter subtitle in "not full screen" "window mode"
all work the best..
i'm set a full screen .
the movie work fine
but now talks in the background but when they start to talk the subtitle show up and the the movie looping itself until the subtitle gone ..
but without subtitle it work perfectly.
how do i fix it/? ive been tried to uninstall all codecs and reinstall them.