GNOME bug 120705 points out that Metacity doesn’t allow users to put a button into the titlebar twice– so, for example, you can’t have a close button on the left and also on the right hand side.
There is no particular reason for this: it was merely an artifact of the original code which has been preserved. However, not allowing a button to repeat has a possibly useful side-effect of providing an upper bound on the number of buttons which can appear.
Is there anyone out there who would actually want to put a button on the titlebar more than once?
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