I had a similar problem last summer when the temperatures in the house reached 40C.
My "upside-down" fridge was freezing all of the vegetables in the crisper bins located in the bottom of the fridge section. I suspected that it had something to do with the freezer located immediately underneath.
I defrosted the whole fridge, and cleaned it... no further problems....but no weather quite so hot either.
Stevo
June 2009