brundlefly
In summary, this was an Output problem not an Input problem. It's possible the OP encountered some other bug I haven't seen, but I don't see how it could be the bug you've referenced, though I've confirmed that bug persists in Platinum.

Ah thanks for the clarification, I missed that detail previously. There are definitely still all sorts of weird things going on with MIDI in Sonar. It would be good if the OP can try to repro it and then log a problem report.

For whatever the worth, I occasionally will manually layer midi tracks, by turning Input Echo On on for the ones I want to stack up.  I frequently do this with things like multiple electric piano layers, or piano/strings coming from different tracks.
 
When I DO the above, Sonar will leave these other midi track Input Echo On buttons ON, when I click on a different midi track to bring it in focus.
 
So, for ME, if I manually am turning Input Echo On 'On', then I sometimes forget to turn the other layers of it off for the other midi tracks, as at that point I am likely experiencing your issue.
 
When I do NOT manually play around with Input Echo On, and rely on the Sonar default setting to automatically turn it on and off when bringing a midi track into focus and then bringing a different one into focus, and operating this way I have no issues where any undesired midi sounds are heard.
 
I don't know if any of the above applies or is helpful - but this has worked for many many many years for me this way in Sonar and its predecessors.  
 
Bob Bone
 

robert_e_boneI don't know if any of the above applies or is helpful - but this has worked for many many many years for me this way in Sonar and its predecessors.  
 
Bob Bone

Bob, I think most common MIDI workflows work in Sonar (although see for instance the linked to video of the broken dim-solo functionality).
 
But things really start going south if your MIDI source is the output of a VSTi. Apparently not many people use this feature or more people would have been complaining about it. It has been broken since at least 2005 when I first noticed this with JMT Orchestrator, and then mostly fixed in X3d, 8 years later. [Yes that was a typo, lol - fixed]. Eight years for a feature in Cakewalk/Sonar to be broken to the point of being unusable. I have old emails from CW telling me it has to be the plugins, the issue isn't in Sonar. Oh really?
 
It sounds like in your case, the MIDI source is an external MIDI keyboard (please correct me if I'm wrong), so you might not experience any of these issues.

Last night I was able to gain control over these tracks by carefully checking ins and outs of MIDI tracks. The issue for me is not to leave MIDI Input assigned to "All" and make sure that it assigned to Launchkey Midi ch. 1. What is Omni, by the way- is it a synonym of "Any"? It worked, but at a moment of this post, it was sending notes to 2 tracks instead of one and I checked in/out settings on those tracks repeatedly. I am not perfect, I make mistakes and learn as I do it. Some time it is an operator error, and some time it is not. I will update as it progresses- I have about 30% of the song done- I will load it more and see if it gives up. I got distracted with another issue last night- see my thread, "I crashed New Sonar"- another MIDI crisis.  

Omni means all MIDI channels.

MIDI Omni is the default for a new track (will accept input from ANY MIDI channel), but can also be one's nemesis. Any armed/echoed track will record/respond to any MIDI input into SONAR with that enabled. Solutions are to disable Auto Echo (when applicable) and only intentionally echo tracks you want to respond to input (if left "Omni") or assign a track to only receive a certain MIDI channel (which can be adjusted/paired on the MIDI controller). Depending on what you are doing, certain methods may be preferred over others, but this is important to realize when working with MIDI (especially plugins with "MIDI through" which will potentially allow them to trigger other VSTis).

SilkTone, 2005 till 2013 is eight years, not eighteen. Not saying it's right, of course :)

Sanderxpander
SilkTone, 2005 till 2013 is eight years, not eighteen. Not saying it's right, of course :)

 
Haha, yes I realized my mistake as I was lying in bed this morning. I got mixed up with how long I've actually been using "Cakewalk". Fixed now. But still - eight years is a long time!
 
EDIT: Especially embarrassing since I highlighted that it wasn't a typo when in fact it was, lol.
 
EDIT EDIT: I just went through my old music app archives and realized that I actually bought JMT Orchestrator from CW as a 3rd party special offer in 2005. Yet it was never able to work right in Sonar. Go figure.

Omni can mean different things in different situations. The MIDI spec only allows for 16 channels total, which was sufficient at the time. The spec also includes "omni", which means to respond to all 16 channels, instead of just a particular channel.
 
However in today's DAWs, 16 channels are woefully inadequate. To get around this problem, the concept of MIDI "ports" was introduced. It is not part of the MIDI spec, but each "port" is a single unique MIDI spec implementation with its own 16 channels. So within that port, omni means just those 16 MIDI channels in that port.
 
So when we say "omni", it depends on the context. If you look at the input selections for a MIDI track in Sonar, we see something like "All Inputs > MIDI Omni, ch 1 to ch 16", as well as "[Your MIDI controller] > MIDI Omni, ch 1 to ch 16". Your MIDI controller is a single unique MIDI port, while a VSTi's MIDI output is another single unique MIDI port.
 
When you select "All Inputs > MIDI Omni", you have effectively selected all MIDI channels in all ports combined. This includes all MIDI output from all VSTis as well.
 
On the other hand, if you select "[Your MIDI controller] > MIDI Omni", it means only those 16 channels coming in from your MIDI controller. Similarly if you select "[Some VSTi's MIDI Output] > MIDI Omni", then you selected only the 16 MIDI channels coming out of that VSTi.
 
The long standing MIDI crosstalk bug I mentioned had to do with the MIDI output from any VSTi bleeding into the inputs of any other MIDI track while it is recording, no matter whether you selected "[Your MIDI controller] > MIDI Omni" or not. Selecting "[Your MIDI controller] > Ch. 1" for instance helped a bit since the MIDI wasn't blatantly bleeding into that track anymore, but it did keep cutting notes short on the track that was recording so it still made the whole thing unusable.
 
I have some questions for the bakers:

1. Is it really that hard to get basic MIDI routing right?
2. One would think this is fundamental in a modern DAW and should be rock solid, no?
3. Why are we still struggling to get a solid Sonar MIDI implementation in 2015?

this is STILL not fixed :(  

Basic MIDI functionality, still broken for 5 years now.