Okay, I've done some experimenting and the issue appears to be resolved.
But first let me say to Charlie, great video man! Have you made others? If not you should. That was a very clear and concise explantion of basic drum programming in PRV.
Now back to the issue I was having. The difference between what I was doing and what Charlie shows in his video is that, from the "Notes" menu in the PRV, I have "Show Durations" unchecked, and "Show Velocity Tails" checked, which shows the little triangles with the vertical velocity tails instead of the rectangles as you would normally see with a non-percussion MIDI track in which duration is relevent.
When I swapped the display to the rectangles, lassoing worked correctly as it always has. And now for the real kicker, I set the note display back to the little triangles with the velocity tails and now lassoing is working correctly with that as well. I've tested over and over and lassoing snare notes just as I described above is no longer picking up kick drum notes down below the selection rectangle.
This tells me that I ran into some little quick that screwed up the lassoing and resetting the note display has somehow "reset" it and all is well.
Thanks again for your help Charlie and once again, great video!
JTW