I tried to reproduce the problem, but to no avail. You can find attached an accessible editor toggled to full screen under IE and the toolbar is being render as expected on my end.
It would be helpful if you could provide more details about:
Are there any JavaScript errors in the console, when the described issue occurs?
Can you versify if the used version of RadCotnrols is 2103.3.1114?
Can you verify if there some CSS or JavaScript customization that could lead to the described behavior?
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