Inconsistency between metro light and dark themes

Hi,

I noticed a difference between the metro light and dark themes for the ribbon. In the light theme when the ribbon is minimized and you hover over a TabItem, only the tab text changes color. In the dark theme, the text change color but I also get the tab border's drawn (the top,left and right borders). This is rather ugly and I would like to get the same behavior as with the light theme (i.e. no borders being drawn).

This can be reproduced using your ribbonpad sample.

How can I go about achieving that?

Thanks in advance!