Ah, it seems that I was mistaken! The problem was, in fact, on my side, rather than an issue in Panda. ^^;
I put together a simple test-program, as you requested–and it worked just as expected. The joint updated its rotation, and all seemed well.
Uncertain, I returned to my game, and the code that handles doors (so to speak 
). I’m not sure of quite how I ended up with the joint’s rotation seeming unchanged–I presume that I made some mistake in where or how I added the test-output. But more to the point, I remembered that actors don’t update immediately after being told to do so, unless forced otherwise. And indeed, calling “Actor.update(force = True)” before I mark the collider as “dirty” seems to solve the problem! (I imagine that marking the collider as “dirty” at a later stage would also work.)
In short, I believe that I have the issue fixed!
Sorry for the trouble! ^^;