Problems rendering small border-image in Windows

[droneone]

Hi all,

I'm having an issue with rendering a small border-image on Windows only using Qt 4.8.1, it renders properly on all other OSes, and I'm wondering if there's something I'm missing.

See attached images, the Windows one has vertical lines through it that look quite bad, but the OSX one looks perfect.

windows.pngScreen Shot 2013-03-13 at 11.09.15 AM.png
The images aren't scaled at all, they are 13x13px PNGs, and here is my QSS code:

QPushButton {
 
    border-image: url(img/led-blue-off.png);
    border: 0px transparent;
    min-height: 13px;
    max-height: 13px;
    min-width: 13px;
    max-width: 13px;
}

QPushButton {

    border-image: url(img/led-blue-off.png);
    border: 0px transparent;
    min-height: 13px;
    max-height: 13px;
    min-width: 13px;
    max-width: 13px;
}

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I've tried numerous options for border-image, with no real effect (other than distorting the image).

Any thoughts on how to resolve this? It's only a problem with these circular images, other images in the 15x15 to 13x20 range work perfectly.

TIA!