FLV stops, loops, rewinds on iMac

I am running an flv in the MediaDisplay component (with MediaController), using cues to advance the related SWF frame by frame. No problem on Windows, but particularly on iMacs with OSX.x the movie will suddenly get caught in a loop or rewind to the beginning. The streaming bar shows that the flv is fully downloading, so it is something in the interaction with the SWF. Happens in both IE and Safari. Does not happen on a G4 or old iMac with OS9.x. Does not happen in Windows.

The problems always occur after the FLV has played for 51 seconds.