Recently there have been an increasing number of reports of unreliable video playing. I have identified a number of problems with omxplayer and hopefully added workarounds for them in Pi Presents.
If you run this version of Pi Presents from a terminal window you will see reports of the workarounds in action, even if debugging is turned off. omxplayer probably goes wrong one in a few hundred plays of a track on average and always at the end of a track.
I hope I have caught all the problems. I would be interested in any other undetected crashes of Pi Presents when playing videos as I may not have discovered all the failure conditions.