Use VLC or/& MPlayer with in-built codecs & no need to worry about QuickTime bugs or downloading extra codec plug-ins for QT.
In video editing circles, it's not uncommon for there to be bugs in new QuickTime releases. In recent times, Apple seem to be concentrating on making QuickTime & iTunes for their commercial aspects of buying online, and less emphasis on making sure of high quality & lack of bugs exist for programs that utilise QuickTime, including the QT player itself.