Emu XL-7 & MP-7 User's Group

I've been using Live as an effect rack and driving it from the PX-7
using the PX-7 as the master clock.  Today I froze a couple of synth
tracks to free up some CPU and was surprised to hear them glitching
heavily.  Since the problem seemed to go away when external sync was
disabled in Live I fired up Logic and watched the Logic midi clock
bounce all over a three bpm range while syncing to the PX-7.

Is this normal?  I seem to be getting a very unstable clock signal
from the PX-7.  I tried a separate midi cable to rule that out and
also an empty pattern with no midi data at all on the PX-7 to make
sure it wasn't just a case of choking on too much data.  Neither of
these fixes made any difference.