If you've had her checked out for hips and knees it's probably nothing. Shelby had a funny gait that I assumed was puppy clumsiness...turned out she had a bad knee. But since that's been ruled out...I'd say it's just puppyhood. Shelby is the one that sits funny. When she sits on the kitchen floor her back legs slide out. She'll be sitting with one leg stuck off to the side (nothing to do with her knees...they are fine now). Seems like she's just more comfortable that way. She is also lays "froggy legged" style whereas Jake never lays like that. He's always on his side.
Loving mom to Jake, Shelby and Micah