Using the smart tool in the PRV as per help file, Right click+drag is supposed to lasso select notes, but sometimes when doing this, I see the selection rectangle as I drag around the desired notes, but when I release the mouse button, no notes are selected and the context menu pops up as if I'd simply right clicked in an empty space. I can't come up with any specific scenario or repeatable set of actions that caused the behavior consistently. I just tried it about a dozen times alternately selecting two different sets of notes and it happened probably three times. But other times it will keep happening repeatedly and won't return to normal until I (seemingly) randomly click some other element in the interface.
 
Any one else experience this?

I don't think this ever happened for me.
 
It may also be a hardware problem of the mouse.

Yeah... sounds like the Right Click button is triggering again when you release the lasso selection. Try another mouse or be aware of any user misfires on the right click button. It's easy to accidently click again when releasing.
 
Cheers.

Yeah, I think you guys are right. I'm suspecting the mouse as well. At first I didn't realize that a right click by itself would deselect the selected notes, but it does, so Beepster's hypothesis makes perfect sense. A second right click trigger would deselect the notes that I was selecting (instantaneously apparently) and then bring up the context menu. I really think it's probably this cheap wireless mouse/keyboard combo I'm using, sometimes the keyboard gives me trouble too. 
 
Thanks for the input (no pun intended), looks like I'll be purchasing another mouse/keyboard, hopefully higher quality.