While my mechanical knowledge of the CVT-type transmissions is hazy at best (they function in a manner that is fundamentally different than your average automatic transmission), I can tell you that this is not a normal behavior.
Part of the problem may be that they arent able to duplicate the problem (I'm assuming that you haven't taken it to the dealership during weather that would cause it to "skip"). Your best bet is probably going to be to have it towed to the dealership on a sub-zero and/or snowing day, and if they cannot duplicate the issue themselves, have one of their technicians ride shotgun while you drive, so they can get a taste of what's going on.
Sorry I don't have a better solution for you, but I would like to wish you the best of luck!