Generally I have more problems in the front than in the rear but icing can cause problems with both. Usually the back one frees itself after awhile. The front sometimes requires a whack with my boot and a good cleaning.
Ghost shifting can be caused by a number of things including a derailleur slightly out of adjustment or sticking. If you have an opportunity, give your drive train a good cleaning and re-lube to see if that helps. If the loop of cable right near the derailleur is too short, that can cause problems too, as well as a chain being too long.
I think jagwire has some sealed cable ferrules that may help keep the cables from freezing up. I may invest in some for next year.