THE PHANTOM SELECTOR, or, the Ghost in the Machine:
It has come to my attention over the last month that some Montanas are self-selecting menu items and going into Map Scroll mode on their own without any user input. A friend's 650 has an extreme case where it just keeps making menu selections until it reaches a screen where it can't go any further, then won't let him make menu selections back to the map or anywhere else he might want to go.
These videos show the problem.
The issue as I see it is heat related, and seems to happen mostly when stopped in full sun. I think the screen protectors which come with the Garmin Rugged Mount get hot, then exert pressure on the touch screen, causing strange behaviour. If you happen to be on the map screen, it'll likely go into Map Scroll mode. If this happens while you're travelling, it will look like your screen is not updating itself. To check if this is the case, look for an arrow at the bottom left of the screen. If you see one, you're in scroll mode. The normal map screen has an X in the lower left, not an arrow, as seen below.
This is not a fatal error, and in my case, once I start moving the problem goes away but my buddy said his was doing it at 130kph.
It may be worth trying the unit without a screen protector to see if the problem persists.