My best guess is JCE isn't properly destroying itself. We call Joomla editor JS functions and TinyMCE JS functions for an editor to be cleared, but JCE isn't using Joomla standardized API so it's problematic as I've no idea what JCE API is to do this.
There's no API documentation so I don't know when I'll be able to fix that as I've to set aside the time to dig into JCE JS and figure out how to safely destroy an editor. I just don't have that time right now. I've created a bug ticket regarding the issue.
forge.joomlapolis.com/issues/9254
If you could provide exact steps to reproduce the problem reliably that would be of large help as well.