UAD Fairchild playback weirdness

When I put the Fairchild 670 on a stereo bus, it moves the spatial location of the instruments.  For example, I put it on my drum bus, and it widens the overall sound (may be good or bad, depending...), but ALWAYS moves the snare to the right, no matter what preset.  I can tweak the settings all day, but the snare (and sometimes kick) move to the right.
 
It's made this expensive plug basically unusable (unless I change the bus's interleave to mono, which I don't want to do).
 
IKM's 670 emulation doesn't do this.
 
I've checked all of the levels in Sonar and everything is as it should be (namely, the pan pots).  And, again, no other plug does this.
 
Has anyone experienced this or have any thoughts?
 
Thanks in advance.