I have two MIDI tracks on Tracks 12 & 13 (see image below).
 
I can edit Track 12 normally.

On Track 13, I can only add or remove individual notes. I can't drag the clip anywhere, and I can't copy paste. I thought I might have accidentally locked the clip, but it isn't showing up as being locked. Bouncing to clips didn't help. I can delete the track and start over, but I'd like to know what setting I changed to make the track behave this way in case it ever happens again. 

Any suggestions? Thanks. 

Well, I "fixed" it, but I still don't know what went wrong.
 
I deleted the track, then did an Undo Delete. When the track came back, I could copy/paste and drag it.