Can you please let us know whether the top level pages are actually group pages? The probelm is that currently a group page is redirecting to its first subpage, but the current page still remains the group page, that's why VT Difference doesn't get highlighted, since it's not the selected page. We have logged this issue for implementation, you can track its status and vote for it in PITS on this public URL.
Please excuse us for the inconvenience this issue might be causing, as a workaround until we implement this functionality you can convert the Architectural Wood Doors page to be a redirect page, not a group page, and set it to redirect to VT Difference.
the Telerik team
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