I agree, I think the plate is part of the mount and the rubber separated from it. The more I think about it, I believe the bolt snapped inside the rubber bushing. Here is a picture of my motor mounts:
I am replacing the bell shaped housing (Rubber Motor Mount Heat Isolator) and the rubber bushing with the solid motor mounts from Backdraft. Now that I look very closely at the above picture, I can see there is what appears to be some kind of plate at the bottom of the rubber bushing.
I'll post more info as I figure this out.
Thanks.