I've just (in the last 2 weeks) changed out two Hengst filters--no problems of deformation.

Changing filters, you're supposed to blow compressed air through the center tube, to make sure it isn't plugged. I suspect most people don't do this. The first time I did, it took me a half hour to clean the tube out.

Jim's analysis could well be right (too complicated for me), but the first thing I'd do is make sure the center tube is clear.