Okay, got a good one here.  Running Cubase, Win7 Pro 64 bit. 

If I map the Cubase stereo output to UFX AES left and right (software playback), the AES left channel is showing overload, even thought the signal is no where near overload level.  The channel meter displays correctly (well under overload level), but I get the red overload indicator at the top of the meter, and the "UFL" text changes to "OVR".  This happens regardless of what level I have the Cubase output set to (if the output is muted or the fader in Cubase pulled all the way down I don't get the overload, but as soon as I bring the fader up even slightly, the overload hits).  If I take the exact same output and map it to ADAT playback channels, no overload.  Now, here's where it gets interesting...

If I flip the channels (Cubase left to AES Right, Cubase right to AES left), I still get the same overload on the AES left channel....It doesn't switch to the right AES channel.  Further, this only happens when the UFX is connected to the computer via USB.  If I connect via firewire, everything's fine.

Obviously the overload indicator is not displaying correctly, but why?