iZotope Neutron + SONAR Aux Tracks

So I've been playing around with Neutron Advanced, and I'll admit, it's kinda cool. One thing I've noticed, though, is that the masking feature doesn't seem to work with Aux tracks. 
 
For example: I have two rhythm guitars feeding an Aux. Then solo electric guitars on separate tracks. Neutron is placed on the Aux and both solo guitar tracks (three instances).
 
The track assistant works across the board, analyzing the audio and suggesting a preset for a starting point. The results are hit and miss (and sometimes it doesn't automatically detect the track as guitar/instrument) but some of the presets are very usable.
 
However, if I select the Aux instance of Neutron and select one of the solo guitars with the masking tool, it shows no masking at all, even at the highest sensitivity setting. On the other hand, if I select one of the solo guitars (audio track, not aux) and pick another audio track, the masking tool works perfectly.
 
Anyone else notice this behavior?