Interesting. I have a test project that I created to demo the loop-sync issue for a bug report. It loops a MIDI-driven instance of Session Drummer 3 against bounced audio from the same track. The loop is not exactly on measure/beat boundaries, and the two tracks drift out of sync at the rate of about 9 samples per iteration.
I just tried changing the gain on the live track, and indeed it drifts out significantly faster. I haven't measured the drift rate precisely, but I'd estimate it to be 4-5 times as high based on how many iterations it takes for the sync error to transition from sounding like a phase error to sounding like distinct hits (i.e. around 10ms).
Incidentally, I was never able to reproduce this sync problem with loops on beat boundaries, and I still can't now, even with the altered gain.