With the comb filtering comment--haven't noticed that here either, but one thing I thought might be worth mentioning in case it happened to be in play here. I've noticed if you use two cabs in a preset and one of them has a 'non zero' motor drive setting and the the other has motor drive on 'zero' it can introduce weirdnesses--With both cabs motor drive "on" or both cabs motor dive "off" no problem... Has made me think that the motor drive processing may introduce a slight delay....Anyway, probably not the issue, but you never know...