Beer and physics

[GT40FIED]

Alright...here's a brain teaser for you unworthy maggots. A few days ago I put some beer in the fridge since it'd been in my truck all day and it was a warm day. I left it in a bit too long, but not long enough to make beer smoothies. There was a bit of ice in the first one, but nothing major. As I worked my way down to the last one (#6) the beer had been out in the air for long enough to have thawed. However, number 6 was frozen solid. I can't figure out how this is possible. Upon removal from the freezer, the can should become endothermic (or exothermic depending on how you want to look at it). Either way it should be trading the cold of the freezer for the warmth of room temperature (roughly 68...but my HVAC system is fucked so who knows...but it was comfortable in here). And I'm sure it wasn't frozen solid when I took it out 'cause I lightly shook the cans to make sure I heard sloshing (meaning they were still liquid). This isn't really all that important, but if someone could shed some light on this I'd be interested. I'm really more confused than anything. Did I just invent the self-freezing beer can?

Oh...and speaking of beer...time for my drunkening. W00t.