Using x7A with automatic flash



I have both a 2800AF and a 4000AF for my older AF bodies but would like to use them occasionally with my X7-A. I tried it today with the 2800AF and the flash worked, but in both M and P there were no meter readings at all in the X7-A's viewfinder. The X7A has one additional contact on the body that matches with one contact on the 2800AF. Can anyone explain what is going on trying this. Thanks