For some reason, a TTS guitar track I'm working with is somehow always falling off-key. I thought it started when I built a pitch bend wheel into the beginning of a note, but now I have no clue why it's happening.
 
1) The pitch bend is from, let's say, 2000 to 0 (actual note key), but when that bend was put in, all the surrounding notes fell out of key.
2) I deleted the pitch bend.* Then I carefully verified (playing by ear) that each instrument track was on key.
3) I played the track from the beginning and it sounded fine.
* I also verified in the Event List that there are no remnants of the Wheel left over.
 
But it seems as though, during playback or jumping between a few measures (then playing), it sets something astray and the track falls off key again by 1 note or so. This is very frustrating! These kinds of glitches make me question the stability of the software or audio engine.
 
How do I know if there's a problem and how do I stop this from happening? Any info is appreciated. Thanks!

I don't know why it would have happened, but occassionally I've seen glitches like this.
 
what I would probably do in your case is save the project AS a MIDI file (be sure you have it saved as a regular project file first).
then close MC, then open it back up.
now open your regular project file.
insert a new MIDI track and then use the IMPORT MIDI function to import the MIDI file you saved.
now you'll have some clean up to do becuase it will have imported 16 tracks and maybe not starting with the track you just inserted.  you also need to delete the old MIDI track.
 
see if that clears it up.