Sounds like a combo of excitable pee (oh mommy I'm so happy to see you) and submissive behavior (he knows you are boss). My Peanut and Bandit will do the exciteable pee when I take them out of the crate also, but they don't do the roll over on the back thing. I try to be as boring as possible when I come home to take them out of their crates, but they still pee. They are young and I know they will outgrow this. My 8 yr old, Harley, did the exciteable pee & roll over when I would come home and he wasn't in a crate! He did this up until he was three yrs old although he was completely house trained.
As they say, "this too shall pass"
