Do you think he's getting ready to shed? When some dragons are in full-shed mode, in the
bath they inhale extra air and puff up so their back legs float. They do this to stretch the skin on their tummies and backs so it will split to shed more quickly. Some of them, like my Richard, keep one front foot on the floor of the tub, lifting the other three so they tilt to the side like they're going to capsize. Then when we get them out of the water they have to do this weird hissing thing to get the excess air out of their bodies.
Or it could be that he isn't comfortable with the
bath floor and touches it with as few feet as possible. Richard would levitate if he could to avoid touching the green reptile carpet that borders his tile.
If he's walking normally in other situations, there's probably no reason to worry.