When using the emu movies for previews, it feels like MaLa is not closing the .avi file and releasing the file handle.
To test it - select an item with a preview movie, let it start, then select a different game from the list which starts a diff movie. Leave MaLa open, and using Windoze, try to delete the first .AVI file - it is no longer active in MaLa, but you can't delete it without quitting MaLa first.
can anyone else verify this on your install?