I'm surprised that I haven't seen this here already—I hope it's not just me!
I've tested the following using DVDpedia 5.0.0, 5.0.1, 5.0.2, and 5.0.3 beta 15. This happens for all versions except 5.0.0:
When using Full Screen Mode entries with more than one linked file will not execute either of the DVD Player or VLC applescripts. In this case selecting any of an entry's files will result in nothing happening visually, but DVDpedia will update the play count and last played date of the entry—however, it won't display the updated date in the Last Seen column.
This is reproducible on demand on a Mac Pro (10.6.8 ) and Mac Mini (10.7.2)
DVDpedia: Full Screen playback broken
Re: DVDpedia: Full Screen playback broken
Thank you for the bug report, a few users reported it via email and it's now fixed in the latest beta of DVDpedia and will be in the upcoming version.