gmp
There's a bug with midi recording that's been around since 8.5. I use the feature "allow recording without arming track". So if I record a piano, then decide I want to record a spot on my drum track and record that drum part and then move back to piano, many times it will record the drums instead of piano.
 
The workaround I use to get Sonar out of this confusion is to hit solo on the drum track, then all of a sudden the record button will light up and I can then turn it off, then turn off the solo button. Then everything returns back to normal. I wish this would be fixed.