Same issue for me. he wont do any of his caster stuff in bear form (which is fine) but i can't get him to drop bear form (which isn't so fine) unless I ask him to wait somewhere.
If I do ask him to wait somewhere, he drops out of bear form but as soon as I ask him to come with me again he, instantly goes back into bear form and I'm back to square one. It wasn't a big deal to clear out the goblins but it was annoying that he wouldn't work as seemingly intended.