I've got a work-around, in the form of an old save, but I thought this was worth reporting:
I'm now doing the (wretched; dragon form has REALLY turned me off of Divinity, because being one-shot just sucks) entry Hall of Echoes stuff. I've been saving and returning to my Throne Room pretty much obsessively. One of the more recent times I went back to my battle tower, I appeared there as a Dragon. I went back to the Hall of Echoes, but appeared as a human. Now, I appear as a human. Everywhere. An attempt to use my stone in any location returns "You cannot shape-shift here."
I've just had a lovely stroll along the floor of the Hall of Echoes. And I'll have to go back an hour, to before I took out two Nest Daises, to hit the last time I was able to be a Dragon. Which I'm honestly not keen on doing.
Forum members and the support team here are quick and friendly, but the number of game-stopping bugs I've encountered is really astonishing.