Mounting Clip - Wireless VDB

[Nanookie]

My AVD2001 fell off bracket today. The bracket is still mounted to wall, but somehow, the DB unit "popped out" of the bracket. 

When it it the ground (DB still works fine), there is a small plastic clip located on the top of the unit that popped out the slot that it sits in. It does not appear to be broken, but when I try and put the clip back into the unit, it wont stay. In fact, it slides down into the hole in such a way that it cannot lock in to the opposing clip on the bracket on the wall. the plastic clip just slides around in the hole. Its almost as if there should be a spring or something else that elevates the clip to a certain level so that it can lock with the bracket on the wall. 

Ignore the marks on the AVD unit where the clip fits in, it was crapped up while I was trying to slide the clip out. 

I dont know how to fix this and I cannot get it mounted back onto the bracket. 

Any ideas? Help? Arlo?