Just when I don't have time and need to finish this project today, I get unexplained issue.
I entered 8 measures bass line via piano roll and need to paste it 20 times with Paste Special. I did it once, it worked fine but one bass part was too low, so I used "Undo" for paste, then changed one part (one measure), copied it again, want to paste it again but it would not Paste. I set it to the same settings I used: I tried "Align to Measure" checked and unchecked. It just wouldn't paste! I restarted Sonar, then I restarted computer- still not doing it. Do I need to make another track and start over? Still I don't understand what I am doing wrong. Thank you.
 
And I started over on a new track, and it still would not paste it!

I had to use Copy Special to make it Paste Special, so ok. BUT: I have it set to paste in track 84, but it pastes in track 85 (creates new track). First time I used undo, did it again and it pasted in 84, but now it continues create new track, even through it set to Paste to 84, not "New". Paste was always broken, not realizing how much it broken until actually using it and working under the deadline.

Are you working in the track view or the PRV?
 
Assuming it's not an actual bug, either it's not getting copied or it's pasting to a location that's offscreen.
 
- Make sure Edit Filter is set to Clips
- Use Copy Special and make sure you're copying Events.
- In the Paste Special dialog, make sure Starting Time and Track and 'What to Paste' are correct.
 
If all else fails, try Ctrl-dragging the selected section to copy it, then Groove Clip it, and roll it out. Or just roll it out from where it is.

I don't know if I know what I am talking about here but this copy paste in PRV mode issue has reared its ugly head more than once for me.  One thing I did ascertain is that if I paste and don't see the data on the track that I thought I was pasting to, I hit CNTL Z immediately to undo the paste to no where.  I think that this has created the double note issue for many a user over time.  The CNTL Z defense has stopped my double note issue in its tracks (no pun intended).
 
But, I find that if I do a SAVE of the project and then try the copy paste that it then starts to work 75% of the time (or so)..... if it still doesn't paste after the save, I exit SPLAT and re start it and then do the copy paste which seems to work 100% of the time.
 
Is this a bug?  I think so but I can't make it happen, it just starts on its own and once it goes bad, it stays bad until I do one or more of the above actions to get it to work again.  
 
Quite a nuisance, but since I can't replicate it, I can't blame the bakers.  But it does make me think, don't the bakers use SPLAT themselves so they to can run into this problem?
 
Hopefully, this will help you.
 

We will keep an eye out for this, but in the interim, if anyone comes up with a solid repro, let us know.
Thanks!