Mine does that too.. Only when she is swallowing though. She'll stand straight up and wobble with the rat in her mouth and still a little as it has slid down her throat.. I think it is just her muscles working the rat down the digestive track myself.. but I'm no expert.. I just know she doesn't wobble at any other time..
When a BP swallows a rodent it throws the center of gravity way up in the air. This will cause them to wobble. It's physics not the snake. Nothing to worry about.
Wobble associated with the spider morph is caused by a neurological issue and is very different.
I'm fairly positive they're both just regular bps one was purchased from pet smart for 70 bucks is a few months and is perfectly healthy. The other is a 3 and a half male (not sure how old) and was bought off Craigslist (with RI which is being treated now.)