How do i get rid of this annoying line at the end of the QTabWidget

Question

So i have a fairly simple style sheet to change the look of the tabs in my Qt app (i'm using PySide, but it shouldn't make much, if any, difference); here it is:

QWidget{
    background: gray;
}

QTabBar{
    background: gray;
}

QTabBar::tab {
    background: lightgray;
    padding: 10 10 5 10;
    font-size: 14px;
    color:  gray;
}

QTabBar::tab:selected {
    background:  gray;
    color: white;
}

If i just use this; then I get an ugly line at the end of the tab - like this: (this is the top right corner of the app - if you resize it so that it goes beyond the size of the tabs)

If i add the following CSS to the style sheet:

QTabWidget::pane{
}

i get this:

which may look like it fixes the problem, but it does not -

here is the same against a different coloured background:

I then thought that perhaps it was the other lightgray color in use, which would be better, since i want that part to be lightgray anyway, so I changed the colour of the QTabBar background to lightgray.

Still no success.

The colour of the line is neither gray nor lightgray, yet those are the only two colours I use.

How do I get rid of this line?

I would rather a style sheet solution, to keep it out of the program initialisation - as that seems like a messy solution.

Edit: this is using qt designer, and qt 4.6.2. I cannot upgrade the qt version easily.