I too have this problem, but I have just managed to fix it at last !!! Seems that the synchronisation only goes horribly wrong when there is a tempo change is the song. The way I got round it was by altering the bar settings, so that instead of (say) telling BIAB to reduce by 5% I put in an actual tempo to reduce to (e.g from 96 BPM to 87 BPM) then back to the original tempo (if required) a few bars later. This gets round the problem and the sync between real drums and any midi instruments is perfect. Give it a try!