364.12/vulkan: garbage in smoketest window when it is covered by another window

Screenshot here: http://imgur.com/oSVP5Wt

Basically, this is running the LunarG Smoketest exmaple in a full-sized window,
with another smaller window in the foreground. When this small window is moved,
parts of the smoketest aren’t animated (see garbage below the small window in the
shot). When I move the smaller window down, the lower border of the non-animated
area moves up, and vice-versa.
When the smoketest example is first launched, it creates a more or less quadratic window,
where only the right half is animated, the left half shows some teapots and stuff, but
static.

(Qadro K5100M, 64bit haswell).