Two tracks open in PRV, one selected.   Notes on both tracks.   Controller pane open, and fairly wide, extraneous controllers deleted from the controller pane, so the velocity section is about an inch tall.     Select a note in the selected track.     Click in the PRV to unselect the note. 
 
Now carefully draw around under some of the notes on the OTHER track, in the velocity line of the controller pane.     At just the right spot (where the top of the velocity bar would be for those notes on the unselected track) your cursor will change, and if you click there those unselected notes get suddenly selected!  
 
I have hit this and been puzzled by it frequently, resulting in a drawn velocity being applied to the wrong track;  finally worked out what was happening.
 
Not good ...

Yes, I can reproduce that, and it seems problematic. If PRV View is set to only show velocity only on the active track, the hidden velocity bars for other tracks should not be editable.
 
As a workaround, you can lock other tracks against editing, but that's going to get awkward fast. I usually edit velocities using the hotspot on the note in the Notes pane so I've not run into this.
 
Definitely should be reported with a CWBRN if it hasn't already.
 
 

I'll try.    The problem report form is so irritating ..