There is no public guidelines document or anything similar for the Metro theme. You are able to customize it if you use its XAML (located in the Themes subfolder in the installation folder of RadControls).
Most of the cases you mentioned are expected but we cannot determine them as a bug. The metro theme will be improved and discussed during this queue , so your feedback is highly appreciated. On a side note, there is no logic that select files in the list in the Backstage`s recent documents.
the Telerik team
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