When we insert content using the taskbar 'Joomla' button nothing seems to happen. But then I noticed the content was added to the last JCE editor instance, instead of the on on the opened tab.
So I guess there is an issue with linking the editor button to the right content pane when there are multiple instances of the editor in one view?
Maybe this also happens when extra tabs / editor fields are added to an article./ I have not checked that.