I hope there's a simple answer...
When I try to edit in PRV I have 3 copies of notes stacked underneath each other, I have to move all 3 to have the note changed.
Is this a normal situation?

How did the notes end up there in the first place? Are you playing them via midi or are they prerecorded midi loops?

Hey Steve, welcome to the forum,
I find most of time (but not always) when notes are stacked on top of each other or hidden behind each other its because of clips overlaping in the track view.
Maybe you were dragging clips around in that track and over lapped the ends... a few times .
RSMS guitar brings up a good point though. How did you get those notes there in the first place ? 
If you recorded them, you may be in 'Sound on sound mode" and rather than erase and re-record, Sonar is stacking them on top of each other (like layers). At any rate, If you want to get to the bottom of any problem be as detailed and thorough as possible.
 

Thanks for your help, I'm inputting with a Midi Keyboard,
but I think I stumbled on my problem's solution...
I had both key and channel aftertouch enabled, and I think the program was recording those 3 things separately,
stacking them up in PRV mode.