Re: back legs Well, that sounds a bit strange - sometimes Labradors will have a gait slightly to one side to avoid clipping their front paws with their back, but I've never seen a Labrador actually cross his back legs while walking or running. Or standing. I'm not sure I can imagine exactly what you mean though. Have you had a vet check it out? He might possibly be having trouble with something, maybe....
Re: back legs the vet told me at 10 mths he is still growing into his body and he can't see anything wrong yet but was curious to see if anyone else noticed the same thing.
Re: back legs Keeping the back legs too close together is usually a sign of hip issues. I don't want to scare you but you may want to have that checked.