Comment 9 for bug 868354

Allowing two displays to overlap and show different sized viewports of the same desktop is totally permissible by X11 with RANDR. I can't think of any particular use case where you'd *want* it set up that way, but technically it is a permissible configuration as far as X is concerned. It is more of a question of policy.

While I think I can reproduce it under some circumstances with xrandr, I'm not sure that means we should implement the policy at the X level, or if it just means we have two config tools that need the same fix.