Frozen Pipes

Not usually a problem in May, but I did spend some time yesterday clearing the ice from a frozen water line. It didn't have anything to do with our plumbing, instead the defrost drain line on our Whirlpool fridge had frozen closed.
The result was that during the defrost cycle, all the water was collecting on the bottom of the freezer instead of running down to the drain pan where it should evaporate. This has apparently been going on for a while since the freezer floor was a solid sheet of ice. What tipped us to the problem was the water running down the cold air vents into the fridge where it collected in the crisper drawers.
I'm not sure what caused the drain line to freeze up in the first place. At least it looks nicer after clearing all the ice and wiping down the freezer. I'll probably pop the cover off again in a couple weeks to see if the glacier is returning and if so, we'll need more exploratory surgery to identify the cause.