For windows that use client-side decorations, there is a 20px wide border containing the window shadow. The inner 10px area allows resizing the window. However, the *outer* 10px area also receives clicks even though it shouldn't.

[...]
(grawity) so what I'm seeing here with CSD windows (with latest -git builds of gtk3/mutter/gnome-shell/nautilus/gedit), is a 10px border that resizes the window, and another 10px border [20px total] that doesn't resize but still receives clicks
(halfline) for focused window, unfocused window or both?
(grawity) both
(halfline) grawity: are you using Adwaita?
(grawity) yes
(halfline) weird
(halfline) mclasen just showed me it on his machine too
(mclasen) it looks like it is just broken
(mclasen) gravity: can you file a bug ?
(grawity) sure
(mclasen) I think we just need to input-shape away the part of the shadow that extends outside the resize border
[...]

gnome-shell 3.11.91-22-gfc4bc52
mutter 3.11.91
gtk3 3.11.8-51-ga86ca5c
gnome-themes-standard 3.11.90-13-gf622129
nautilus 3.11.90-7-ge95d4ba
gedit 3.11.91-23-g7931529