Thermostat plate in head, what is it and why is it loose?

[Scany]

So we changed the thermostat on the racecar, and while doing so a large ring (about 3" dia and 1/4" thick, with grooves on outer edge) where the small end of the thermostat pushes against, came out. I dont see it in parts diagrams or any other place. I wonder if it's suppose to be a part pressed into the head and stay there as part of the head. Any solutions to this if it's loose? We just put it back in loose, but as the thermostat opens Im not sure it will stay.

[bmwman91]

Is it the brass bushing looking thing on the thermostat? If so, I would see about exchanging it for a new one. That doesn't sound right.

[Scany]

You can see half of it inside the hole where the thermostat goes in the head here:
http://realoem.com/bmw/showparts.do?model=AF93&mospid=47305&btnr=11_4372&hg=11&fg=15