I have the 5 mode and was experiencing trouble with it changing modes when hitting small bumps. As suggested by someone else on the forum, it appears to happen because the battery briefly breaks contact with one of the terminals. I very easily fixed this problem by wrapping the battery in fine tape (I used plumbers tape) so its more wedged in the chamber. So far, no changing.

For those having this trouble I strongly recommend giving this effectivly free solution a try. Just make sure not to get the battery stuck