I have recently had a new double glazing unit with a cat flap fitted to an existing double glazed back door. The glazing company came round, measured up, and came back a couple of weeks later with a new unit, took the old one out and put the new one in. After they had left, I went to clean the glass and noticed that the unit moved in the frame: there was approximately 5mm gap between the glass unit and the inside of the frame, meaning that as I cleaned the glass, the unit moved forwards in the door.
I called the company who reluctantly agreed to come back as I thought there was a problem. After much grumbling, they took the unit out, applied a layer of self-adhesive foam to the edge of the glass and put the unit back in again. The glazier said that in a long panel of glass (this panel is the height of a normal door), some movement was normal.
Having looked at every other double glazed unit in my flat (in the other half of the back door and the windows), none of them move: they all fit snuggly in the frame. Also, when looking at the other half of the back door in which the glass unit was not replaced, the new unit appears (although I can't measure it) to be thinner.
Can any one let me know whether I should be calling the glaziers back again to complain, or whether it is normal that the unit should move a few millimetres when cleaning it and that putting a layer of foam between the unit and the inside of the frame is acceptable. I'm certainly no expert, but I've not seen this on any other window and my gut reaction is that if they had measured the unit properly, it would have fit perfectly, without the need for "padding". Maybe I'm wrong though?