I've been having trouble getting the hotkey icon changes I make to stick. If there's another icon already on the key, it doesn't always change if I drag another spell/ability onto the key. Sometimes the old icon comes back even after I've cleared the hotkey entirely and then edited it. Note that the actual skill does change, and so does the tip. It's only the icon that won't change.
I've moved Istaria out of the program files directory, because windows system permissions might have been the problem. That didn't fix it.