Questionable Quicktime Movie Sync?

Questioning how accurate and reliable Logic and QT movies sync... Here's the scenario:

Working on a film cue, had a QT moving displayed as float. The dialog track is embedded in the QT movie and I exported it to the Arrange window. No problem there. The volume is turned off in the movie float itself.

In the studio I'm working in, the computer's audio output (for things like QT movie audio, alerts, etc.) is routed to a pair of self-powered mini speakers. So with the volume off in the movie float, we only heard the extracted audio playing out of Logic-->audio interface (MOTU)-->mixing board-->proper control room monitors.

At some point in the proceedings, someone turned up the volume in the movie float window and we were now hearing the dialog track out of the mini speakers as well as the control room speakers. And the two tracks were out-of-sync, flamming.

Curious about the out-of-sync audio, I started/stopped/started/stopped Logic several times and noticed that the sync discrepancy changed EVERY TIME I restarted the sequence.

So I'm wondering if this is an indication that QT movie playback sync is not consistent (and therefore unreliable) running within Logic. Any thoughts or suggestions? Rohan? 😉