Double notes in X3e

This is the trouble when you use Sonar (or probably any other DAW) infrequently; you come back with a great idea, but then can't get it down because silly things get in the way.
This time I'm getting double hits from my keyboard.  This is what it looks like in the piano roll:-
 

 
I'm also having trouble quantizing the above.  I seem to get the best results with 1/16 Triplets, please excuse my poor music theory, but does that make sense?

   The thing about the triplets, working off the top of my head, I think I recall that they're not properly labeled or matched right. 
   Like in your example above, assuming those are 1/8 grid lines, you show 1/8 note triplets. But if your snap is set to 1/8 triplets, it actually snaps to 1/4 triplets. You have to set the snap to 1/16 triplets to get 1/8 triplets.
   Is this what you mean?

I have 2 keyboards attached - a piano via midi into my audio interface (UA25-EX) and my Roland A300-Pro into the PC via USB, but I'm not playing both at the same time!  There are no other connections, each keyboard has only one connection so I'm still not sure how I'm getting these double notes.
The grid above is either 1/8 or 1/16 and the notes are pre-quantised.
I appreciate your help, thank-you!
 

I not two connections from the same keyboard, the only other thing I could think is that you keyboard is sending on two channels, but then there wouldn't likely be more than a 1- or 2-tick difference in start times. Did you go ahead and ensure you've specified only one port and channel as Input?
 
If those gridlines are 16ths, then the four evenly spaced notes would be 64ths. SONAR doesn't offer a 64th as a quantize value, but you can enter 60 (ticks) directly in the resolution field to achieve that.
 
Correction: On second look, I see it's 3 notes per grid step. If the grid is 8ths, they would indeed be 16th triplets.

Anonymungus!
   The thing about the triplets, working off the top of my head, I think I recall that they're not properly labeled or matched right. 
   Like in your example above, assuming those are 1/8 grid lines, you show 1/8 note triplets. But if your snap is set to 1/8 triplets, it actually snaps to 1/4 triplets. You have to set the snap to 1/16 triplets to get 1/8 triplets.
   Is this what you mean?

Yes, I think you have summarised accurately, so I have in fact been using the correct quantisation - that's good news!  The thing that's been making it go haywire is the doubled notes - sometimes you get one either side of the quantisation point, so then you end up with total cobblers.
Still mystified by the double notes but I'm not getting it anymore - I wish I could figure out what I did to fix it. 
Now all I have is all the midi on previous tracks coming through onto the track I'm recording.  I thought if you had the proper track selected and made sure input echo was only on the recording track you'd be alright.  I've recorded 4 tracks OK, now I can't get the 5th to work.  The annoying thing is, I know I've been all through this before.
I would hate setting up one channel per track and I'm sure I haven't had to do this in the past.  On the track the input is set to midi omni from all of the midi channels coming from the UA-25EX and A-Pro (A-Pro Midi In, A-Pro 1 and A-Pro 2).
Thanks for your help.

that double note thing happens to me all the time.  I posted about a few times.  It has been a while but I believe the solution for me has been the first one mentioned above.  On the receiving midi track set the input to a particular midi device and a specific channel.   Here is a post from another forum where the dude said the same thing and it worked for that dude. "I had this problem also. The answer was that my controller was sending MIDI on two ports (i.e. USB MIDI In A and USB MIDI In B). When I selected "All MIDI Inputs" for the input source for the track, it was receiving two sets of notes. You could tell your track to only accept the input from a specific port rather than "all MIDI inputs" or tell your controller to only send the MIDI data on one port. For my controller I had the choice of "USB MIDI In A" or "USB MIDI In B".
Sincerely,
J.L.
You could also go to Devices -> Device Setup, select the MIDI Port Setup. Here you can tell Cubase which MIDI Port inputs to include in "All MIDI Inputs"."