This is Crystal, working on something for Nicholas again.
I have observed that when an editor is a custom field, and thus in a tab other than 'content', the editor-xtd buttons do not work. The modal-overlay is displayed, rendering the page unusable, but the modal sadly is not.
This is a JCE bug, not a Joomla bug, as it doesn't happen with the core tinyMCE editor.
I'm just disabling the xtd buttons for now for this use case, but thought you should know!
Thank you!
Crystal