Using H.264 video it will, seemingly at random, start over in the timeline. So around 2/3rds way through, suddenly you're seeing the first frame again.
These files play fine in QT and VLC or any other media player. This problem can be 'remedied' by closing protools and relaunching, however you risk it happening again any time you import a new video, toggle video track on/offline or toggle on/off play video out of pci-e.
This problem has been discussed and documented at length,a nd has been a known bug more than a year:
http://randycoppinger.com/2011/08/31...video-problem/
http://duc.avid.com/showthread.php?t=290098
http://www.gearslutz.com/board/post-...pro-tools.html
etc
Discussions have suggested this is a 2 gig file issue, however I've been able to close and reopen PT and it fixes the problem with the same file. Also it usually happens in the latter quarter of the file no matter the duration. My files are 8 gig 1080i files and when this happens they always start over well after half way, so one would assume not at the 2 gig mark.
Some people have solved this by converting files to different codecs, however in my specific workflow there often isn't time to wait 2+ hours to convert full length TV shows. I just need PT to be able to handle the files reliably that open fine in Quicktime. I'm not even worried that the codec isn't perfect frame accurate; I'd just like it to not loop back to the beginning.