The keytip for Open is set to "O" but appears as "B". Code example:
<igRibbon:ButtonTool Caption="Open" KeyTip="O" LargeImage="Ribbon\Images\FolderOpen32.png" IsEnabled="False" AutomationProperties.AutomationId="Open"/>
Works fine for other items and hence it seems this might be a bug in the Ribbon code...
Thank you for reporting the issue. We were able to reproduce it and this should be fixed in the release version.