Ok..this is the start of the dreaded frozen door latch....It will do it all winter long...and even more if you don't take care of it now. When moisture freezes inside the door handle and latch you have this problem as you describe. There is a DIY on this site on how to remedy this. But for me it seemed like a pain in the ass, and looked complicated. I finally couldn't take it any longer and took it to the dealer. $550 and it was fixed. New updated part that won't freeze. It worked.. But thats what you're looking at...