Office 2016 ribbon tab issue - faded/greyed/grayed out

Hi

Apologies if not the right place but haven't found a forum specifically for Office 2016 ribbons.

I have a PowerPoint Add-In that creates its own ribbon tab using the CustomUI XML.

For some reason on 2016 it seems to default to being greyed out - the right hand pic below.

Attachment 22716 Attachment 22717

If I move the mouse over it then it is fine and stays fine once mouse is gone from over it.

This seems to happen on Excel and Word as well but only if the tab is in the first position - left of / "before" Home

Has anyone else seen this before and can I do anything about it?

I tried using 2010 custom part vs 2007 custom part but doesn't seem to make any difference.

I have had tabs in the first position with 2013, 2010 and 2007 in the past and they have never done this.

Thanks

Simon