Interesting Royal Gramma behaviour

[Slick Fork]

I picked up a Royal Gramma from Golds last weekend and currently have him in quarantine. He spent the first 4 days hiding under the rock so I haven't been able to see that much of him/her. It's getting quite a bit bolder now and I've noticed some behaviour I haven't seen from a fish before. When he's out in the open water in the Q-tank he swims right side up. When maneouvering under the rock though he will quite often be upside down... almost like he's using his bottom fins on the rock.

He eats pellets like a pig and is fat and healthy looking so I'm not really worried, the first time I saw him hanging out upside down I was a little concerned but now it's just kind of neat. Is this typical behaviour for the breed?