Styling ::tab of a QTabBar element results in style lose.

In my application, I want to style the selected tab of a QTabBar element. What I style is only its background-color, but every time I change its background-color attribute, all the other styles are immediately lost.
At first I thought it was an issue only for background-colors, but then trying more I noticed that even by changing the margins of the tabs, all the other styles are lost. The background-color of the other tabs is set to transparent, padding and borders lost too.

I think that the correct way for QT to behave, should be to leave untouched the attributes that I have not explicitly modified, but for such an obvious behaviour not to be implemented there have to be other reasons or I am missing something.

Is this an actual “bug” or is there something that I did not consider when trying to styling the tabs?

Sorry for bumping but isn’t there anybody that has a clue about this? How come nobody has posted a single comment in all this time...