I tried to reproduce the problem but to no avail. Could you please open a formal support ticket and provide a sample page reproducing the issue? For your convenience I have attached my test page, could you modify it to a point where the problem occurs and send it back?
In addition, if you are loading the editor with AJAX, could you handle the editor's ClientLoad event and try to repaint the ribbonbar, e.g.:
rBar = editor.get_ribbonBar()
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