Edit: Oops. Now, also having same issue in 8.5.5481x64 portable, playing same Vista sample vids. Haven't seen the problem w/ THESE vids before.
Tested same vids in VLC 2.0.7 - played fine, so assume it's a setting or problem that developed in SMP.
Extracted portable-0.8.5.5487-x64 into Clean folder in Vista x64. It's looping (bouncing back / forth) right at the very end of some Windows vids, that I've played many times as test files.
Never seen any stable or dev builds do this before.
Tried it w/ both the included mplayer & also replacing w/ mplayer2 - from the SMP / SF d/l site. Both had same problem.
Tried deleting all files & extracting it again - same problem.
Nothing different about any settings / prefs or the way I extracted, then started this build than any of a dozen others (AFAIK). Logs for SMP / mplayer are attached.