I've recently moved to my parents place. I was cooking with a really terrible gas oven, but now mums oven is a brand spanking fan forced one...
It could be the fan-forced setting - not only does it make it effectively hotter than the temp you've set it at (you'd normally lower the temp by 10-15 degC if it's fan-forced) but the air movement could also contribute to the collapsing. You could try finding the normal bake setting, where the fan is not on?