I experienced this bug the first time in the sewers beneath the slums back when I started playing the game upon release. There's was no official fix back then and the only workaround left charname stuck with her bound items.
A few days ago, I restarted the game and here I am, coincidentally again in the sewers beneath the slums, and Hexxat won't revert to her humaniod form.
Did I somehow miss a patch or hotfix? It's certainly not possible that Beamdog didn't fix such a trivial bug after all this time, right?