The thing is that this is the only time this has ever happened. And read closely, as a sequence the timing is dead on. Only after sending it to wav does a timing glitch appear. The recording is not the issue. The merge to wav is. I have already tried pulling that track back in out of a save to individual wav files (I do that for every song. disc space is cheap. why not?). When I merge it to wav without that one track, it's fine. So tonight's mission is to record that track again and see what happens.

Very strange. 25-ish songs into Real Band and this is the first time I have had any timing problems after merging to wav. And they are both glaring and exponential. The song is 90 bars. The scratch guitar track starts at 9. By 21 it is becoming audibly off beat. By 50 it is very bad, and by 75 it has drifted almost a full beat. And with the tempo at 84bpm, it is really glaring.