Apple Logic Pro /LogicExpress Discussion

Using MacBook Pro
Logic 7
RME 800 fireface.
Mono Output (double signal) - 2nd speaker mirrors 1st.

I play a pattern through the UB instrument plug-in, and everything
works just fine.
However when I drag the pattern into the arrange window, I start
hearing polyphony notes dropped, latency, and other such playback
problems.
When I return in the UB, it has become affected too, and now plays
with the same problems as the region in the arrange window.

I do turn off the UB sequencer after I dragged the loop in the arange
window, to ensure that UB won't play at the same time as the region in
Arrange.

One more thing:
When I disconnect the RME Fireface, the problem stops.
UB is the only plug in this happens with.

What could be the possible setting in the RME that I am not quite
grasping.
I did all of the recent driver updates for the RME.
Could it have anything to do with the fact that UB is either Stereo or
MultiChannel, and problem occurs due to the Monoaural output system?
That wouldn't explain why it works before I drag the file in the
arrange window.

Any help - greatly appreciated.
Cheers everyone,
Adrian