audio/video syncing problem after bouncing

[oplatner]

hi,

i'm syncing an audio & video clips on pro tools 10. the syncing is prefect when i play the project within pro tools video player.
the trouble is, that after bouncing the project to a quick time file ( mov ), i'm playing it on windows media player and i see that there is no syncing between the audio & video.

on older project's i didn't have this problem - today i did an experiment - i've bounced an old project which i didn't have any problems with in the past. guess what ? when bouncing it again today i can see that the syncing is off....

i'm bouncing on 48khz, interleaved file, tweak head.

any idea ? maybe i've changed some settings/preferences without knowing it ??