Since the move to a newer version of VC++ it appears some interface elements have lost their style, the one I noticed right away was tab controls are now just text, they don't have any additional stylization such as the borders around the tabs themselves, and the border around the control itself.
At a quick glance, buttons that aren't flat and have no set border no longer have a "default" button look to them and are just flat squares with text. Probably more, but we've moved away from most DMF stuff where possible.
I have a feeling moving to newer Windows libraries has upset some of the more ancient of the interface controls.
When does the problem NOT occur? Whatever version comes before the VC++ update, I can narrow it down further if needed.

This is a tab control, it ain't supposed to look like that.