Here's something I expected to be able to do:

1. Select MIDI data in track 10 in a Piano Roll view, and cut it.
2. Change the visible track to track 11 via the Tracks drop-down.
3. Paste it.
4. The data appears in track 11.

What actually happens:

1. Select MIDI data in track 10 in a Piano Roll view, and cut it.
2. Change the visible track to track 11 via the Tracks drop-down.
3. Paste it.
4. The data appears back in track 10, in a new clip that is bigger than the pasted data.

How could this possibly be desired behaviour?
 
The answer is probably "it'll go into whichever track is selected in Track View, at whatever time the Now marker is at", but I don't see that makes sense. Unless I explicitly click in the Track View between cutting and pasting, the program shouldn't use that to decide where to put things (as those values become somewhat arbitrary once you've been working in a Piano Roll for 10 minutes.)

Paste will paste to the track that has focus which is different from selection. Focusing the target track by clicking on it in the tracks pane of the PRV will make it the target for the paste. Changing what tracks are visible in the PRV using the track picker does not change the focus.
 
In general I prefer to copy/move notes between tracks in the track view because you can do it by dragging, and it's inherently clearer where things are going because the tracks aren't sharing the same vertical space.

can we mark this as solved?  I can see why this is confusing, knowing the "focus" and all but it works as brundlefly notes...

Point being, why should I need to move to the track view, and 'focus' a track (not that the focused track is very clear from the UI), just to go back to Piano Roll and paste it in? Can I even see which track is focused when in the Piano Roll? And finally, why, if I'm editing track 10, would track 11 have focus - that works like no other program I know. It's ridiculous.

If you use the paste special command Ctrl-Alt-V then the paste dialogue box opens and you can specify the target track.