MIDI file's doubling of notes visible in staff view. What might have caused this?

I'm in the process right now of deleting half of all the notes in a MIDI project of mine. This has occurred only with this one MIDI file.
 
When I open Sonar's staff view to any of the instruments, all the notes are doubled. This actually affects output. The tracks with doubled notes are louder than those that I've edited, removing half their notes. I can play back a track after I've deleted a portion of them and as soon as it gets to the doubled notes, the boost in volume is obvious.
 
That really doesn't bother me too much. Mostly I'm just curious if you might know what caused this. Might I have somehow inadvertently loaded the MIDI file on top of itself? I don't even know how I would do that. But that's all I can think of at the moment.
 
Oh, I should probably also mention that this MIDI file is actually a MIDI backup of a song I originally composed in Sonar. Using the staff view. I wrote it several years ago on a PC that no longer exists. In fact, that PC's hard drive crashed, and I'm lucky to have found these MIDI backups. I don't have any .cwp file or .bun files, and I don't know how useful they'd be on a different system anyway. But since I wrote the tune in Sonar, I gotta assume I used Sonar, probably like v1 or v2, to create the MIDI files.
 
Okay, well, that's it. Meanwhile, I'm back to deleting notes. I'm about halfway through the file right now. Fortunately, there are only six tracks. Coulda been worse. Coulda been sixteen.
 
 

I had this happen when for some weird reason my controller was set as a midi output, anything you played could possibly come back in a loop. I always make sure my outputs are shut off unless I need them. 

I had this issue when the Virtual Controller was introduced into SPLAT, but I’m not sure if that was the issue because, at the same time, I downloaded several 32 bit free synths (can’t remember which ones). Not only did the double notes appear in that vst, but in every other one. It lasted a year and then went away. Cactus Music has a good point about the midi output. I found the “remove double notes” to be less than satisfying. It just didn’t work.

This is how you insert the key Michael.

From the Project menu which is in the top line of the SONAR Window
Select Insert Meter/Key Change

Set the Measure at which you want the key change to occur 1 for the 1st Bar.
Use the meter box's if you want a different time signature
Use the drop down box under the words Key Signature to select the Major Keys
Minor keys are not listed but you really do not need them do you?

Click OK.

It is there because it will affect the entire project.