Physics Constraint Vehicle - Self-Righting but able to Yaw (Twist)

Hello, I’m wondering if someone can help me out with a little problem I can’t seem to resolve.

I’m trying to create an airship or a blimp that’s physics enabled, but will always try to keep itself oriented horizontally level. I’ve managed to get that behavior working using a Physics Constraint, but for some reason despite specifying that Twist should remain Free (so that the blimp can turn when flying), no matter what the Constraint still keeps trying to orient the blimp facing forward in the X-direction.

Am I missing something really simple here? Thanks for the help in advance!