I was creating a bass guitar track this weekend and decided to use my favorite (not!) VSTi, Kontakt.
Upon loading it I discovered I had 54 lanes by default, and thought of this thread.
I did a little fishing and experimenting, (This is why songs never seem to get done BTW.)
I found that I had set the configuration to "Automatically add all instrument output tracks" probably while using another VSTi where I wanted that, and the configurations settings were still that way.
As Greg indicated, and hopefully this clarifies, unchecking that box and only having the main channel box checked (leaving all the "Aux" and "Unassigned" unchecked) as shown in this shot should give you the desired results.