Thanks for all the thoughts, y’all!
@ Walter and @ Brian:
Tried dragging the ProRes directly to New Composition, and I still had the extra frame problem. So that’s out.
@ Ben:
Well, part of the weirdness is that the graphics run normally, but the video has the stopped frame. Which, frankly, I can’t see during playback—it was only noticed by the QA people making the Blu-Ray masters.
But… sure enough, using Interpret Footage -> Remove Pulldown -> SSWWW, the doing everything in 23.976 removed the extra frame!
I am afeared of what this is going to do for timing, but at least I’m a couple steps closer. Thanks, everyone!