I have encountered the following behavior several times today and it seems to be consistant behavior with the latest version:
Load a playlist and start playing it, select part of the playlist and execute a mass tag operation on it, such as change the artist name. When the currently playing song ends and the playlist changes to the next, it skips out of order and goes to the absolute last song in the selection that is being mass tagged instead of the next sequential song if the mass tag operation is still running.
EDIT: correction, original message said that foobar skips to the last song in the playlist, it does not, it skips to the last selection being mass tagged.