Just in case it's not obvious what the effect is, there are steps to reproduce it at https://bugs.launchpad.net/ubuntu/+source/gtk+3.0/+bug/1240957: you just have to run two apps like gnome-terminal and nautilus and try using the mouse wheel to scroll them. nautilus no longer scrolls with the mouse wheel unless it has focus, whereas gnome-terminal always scrolls. Scrolling without requiring focus has always been one of the nice things about X desktops, and now it's inconsistent and broken.
IMHO, this is quite an annoying regression.
Just in case it's not obvious what the effect is, there are steps to reproduce it at https:/ /bugs.launchpad .net/ubuntu/ +source/ gtk+3.0/ +bug/1240957: you just have to run two apps like gnome-terminal and nautilus and try using the mouse wheel to scroll them. nautilus no longer scrolls with the mouse wheel unless it has focus, whereas gnome-terminal always scrolls. Scrolling without requiring focus has always been one of the nice things about X desktops, and now it's inconsistent and broken.