thats nothing to worry about. I have 2 dogs and they both sit differently,one dog sits exactly like your dog but the other on sits different.... don't worry your dog is fine (as far as the sitting goes)
Not only does my dog sit like that ALL of the time, (unless she is getting a treat) when she is in her crate, she will lean back against the sides and put her paws up like she is reclining. I personally believe that she watches her 'daddy' too much and wants to be like him!!! BTW - your doggy is precious.