Ah, someone's finally discovered and reported this
I've known about it for a while, but there's no elegant in-system workaround due to how the scripting, animation, and sound systems are integrated. The animation continues looping the sound until it's complete, and the animation can't complete until you leave the menu.
Thanks, and I'll see if I can find a simpler way to solve it. I think it may work to just cut all audio before the transition--just have to make sure that won't screw up anything else...