When the setting Tab appearance > Advanced tab settings > Do not paint a tab when only one tab exists for the group' seems to behave strangely for me with windows explorer (the only application I have groupy enabled for).

When the setting is on, the tab is still drawn, but when the window is in focus is hard to read; The text is white and there is no distinction between the tab and the background.

When he setting is turned off it appears as expected: 

The description under the setting says 'This is not used for windows where Group is replacing the native tabs'. If this is the case for windows explorer, then I would expect the option to indeed do nothing.

Regardless of if this is an instance where Group is replacing the native tabs, the white text is difficult to read, and so I believe that this is a visual bug.