Could you please specify how exactly you are able to edit the table? I tried this and as far as I can tell you can only select parts of the table, which however does not contradict with the fact that the editor is read only. Additionally, please verify that you are using the latest official version of RadControls for Silverlight - Q2 SP1 2013.
Generally, we are not considering not showing the tab altogether in such cases as it contains information which should be visible to the user such as the alignment of the text in the table cell where the caret is located.
If I misunderstood you please try to provide additional information on the issue.
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