Solid color instead of background image when using FlatStudio gtk themes.

In 2.0.1 of lightdm-gtk-greeter, when the gtk theme is set to FlatStudio (any variant) and background to some image, the image is not shown and instead solid color is visible. It doesn't happen with e.g. Adwaita.
The commit that introduced this problem is http://bazaar.launchpad.net/~kalgasnik/lightdm-gtk-greeter/post-2.0.0/revision/323
I checked the theme files and found that the solid color is generated b the following lines:

* {
    /* inherit the color from parent by default */
    color: inherit;
    background-color: @theme_bg_color;
}

This is in file gtk-widgets.css in FlatStudio. Changing the background-color property here changes the solid color seen instead of the background. So my guess is, there's a fullscreen window on top of the wallpaper which is themed by this line.

I've attached an image showing the problem, left side is with FlatStudioDark, right with Adwaita, for comparison.