I think it's a good idea to store mixed glue in the fridge when not in use. Sure the next warm up time is a bit longer, but dealing with mold is something I can do without.
I recently gave my copper pot a good scrubbing, old darkened glue from the sides of the pot were sort of contaminating the fresh batch I had made and for some reason I really didn't like that. So after dumping as much as possible I stuck it in the sink in hot water and with some steel wool got the pot looking like new again. I'm sure it made no difference to the glue, but I feel better about it.
Oh yeah, the wife really loves the fact that I store the glue pot in the fridge too.