Background behind some windows is not blurred because the invert effect
sets PAINT_WINDOW_TRANSFORMED. This essentially "turns off" the blur and
the background contrast effect unless we set the force roles.
Because the invert effect is a "post-processing"(not really) effect we
don't have to set that flag.
BUG: 279076
BUG: 359583
FIXED-IN: 5.14.3