I wonder if anyone has one of these. When I have extended the isofix points on the carseat and try and get it into the isofix points in the car, the extended bits just slides back in so that I can't install it. I'm used to installing a Britax isofix, so don't think I'm doing anything wrong - this one locks into place so you can put pressure on the points without it sliding back in. Is my seat broken or is this a problem that everyone has with the seat? Thanks!