I've noticed this occasionally happening for a long time (at least a couple of years, I think), where iFly gets skewed while in Track Up mode. Just like you said, if you hit North Up and then Track Up in succession it clears it up. I wouldn't mind it getting fixed, but it's always been just a minor annoyance. I've never paid attention to what happened to cause it, so kudos for finding at least one reproduceable way to make it happen.