DVCPRO HD 720p24 bug - Walter?

I've been searching the forums for any mention if this, but I don't see anything recent.

FCP has a render bug that's driving me absolutely bonkers. The project is DVCPRO HD 720p24. I'm creating graphics in Combustion and exporting them as Quicktime movies with the proper compression settings. When the clips are imported and placed on the timeline they play just fine, no rendering required.

Whenever the imported clips are altered within FCP, such as doing cross-dissolves, opacity ramps, adding a 3-way CC filter, etc. the rendered segments play back with a stuttering motion. Stepping through the rendered segments shows duplicate frames, hence the stuttering effect. It's bizarre. The segments play back the same way both on the computer monitor and on the broadcast monitor (Sony PVM-20L5/1 fed by Kona LHe). As long as the imported clips are not altered, they play back perfectly. Quicktime Player reports the clips as having the proper frame rate, dimensions and compression settings.

I've tried everything to get around the issue. I tried exporting my comps as image sequences, then importing the sequence folder into FCP (making the default still length one frame) and placing the nested stills on the timeline. The exact same thing happens. As long as there are no dissolves or superimposed tracks, the image sequence plays back properly. Exporting the comps from Combustion as Quicktime movies using different codecs (Animation, ProRes, etc.) doesn't change the problem.

The bug does not occur with any of the footage from the camera (DVCPRO HD 720p24 from an HVX-200). Cross-dissolving between the camera-originated footage works perfectly.

I suspect that Quicktime is the culprit, but at some low level that is impossible to diagnose.

Walter, I know you rely on a DVCPRO HD workflow for your projects. Have you run into this before?

System specs:

Mac Pro 2x2.66GHz dual core Xeon (quad core) / 2.5GB RAM / ATI X1900 XT / 2TB 4-drive internal SATA RAID 0 / AJA Kona LHe / latest revisions of OS X 10.5 and FCP 6, all updates applied

I'll try to post some examples on my website when time permits.