Screenshots using GTK+ on Windows: works fine except if monitors are "stacked" vertically.

[kcirtap lavabit com]

I use GTK+ to take screenshots in my program on Windows. It works great;
however, someone reported to me that if their monitors are "stacked"
vertically, the monitors in the top row aren't included in the screenshot
properly (it looks garbled).

I was able to confirm this; I opened up my graphics driver's control
panel, positioned my secondary monitor on top of the main one in the
configuration, took a screenshot using my program, and while the main
monitor (positioned on the bottom) shows up fine in the screenshot, the
secondary monitor (positioned above the main monitor) shows up garbled.

I'm not sure if this is a bug with my program (is there more than one
window besides the root window?) or with GTK/GDK. Any help would be
appreciated.

By the way, I already submitted this as a bug (#634713), and you can view
it, along with an example program demonstrating the issue, here:
https://bugzilla.gnome.org/show_bug.cgi?id=634713