coke and science - why?

[Kryton]

kinda weird, but here goes.

the background:
i had some drinks sitting out in the fridge in the shed. the fridge is known to freeze things if you put anything right up the back.
so i managed to freeze 2 x 2lts coke and a couple of stubbies (didnt explode).
moved the cokes to the door for a couple of days but they were still pretty much frozen so i took them out and left them over night.
put them back in the fridge the next day (in the door) and theyve been there happily staying chilled.

the weird part:
a few days ago, i bought one of the previously frozen bottles inside and put it in the fridge. the fridge is pretty new and hasnt made ANYTHING freeze at all, in any way shape or form (there is no freezer section anyway - its just a fridge).
put this bottle in the door and a few hours later, its half frozen.
im sure it was liquid when i put it there so i kinda brushed it off as maybe it was half frozen?

anyway, today i did the same thing. took the other previously frozen bottle, checked it, made sure it was all liquid and no ice and put it in the house fridge. and ill be stuffed, its half frozen after 2 hours.
there was a 3rd bottle of coke that didnt get frozen in the shed fridge and that didnt turn frozen when i bought it inside either.

so, anyone into science want to try to explain why if you freeze a bottle of coke, defrost it, chill and change it to another fridge it freezes?

the shed fridge is set colder than the house fridge too.