Why won't my Collections save in Bridge?

Hi, folks.

I like the idea of building collections in Bridge based on keywords and whatnot.  That way, I can have all of my images in one directory and simply use collections to browse them rather than having to load every single image in the directory through Bridge.

But...Bridge never seems to save the collections once I exit the program.  The name of the collection, itself, will remain upon a restart, but there are no longer any images in the collection.

This is not in reference to smart collections.

Thanks,

Greg