Resize handle can lead to unintended window movement and jumps

The Gtk3 window resize handle that is in the bottom-right corner of most Gtk3 apps can lead to an unintended window move as well as make the window jump by a huge marign, thus leading to the window being out of the screen. The problem is not perfectly reproducible, but happens around 20% of the time when clicking the handle instead of doing a click&drag. I am using XFWM and Xubuntu as well as a multi-monitor setup, which might be related to the problem. To reproduce:

1) open a Gtk3 app, such as Evince or GnomeTerminal
2) click the top/left corner of the resize handle a few times

Resulting problems:

* The window will be grabbed so that one can move it around, which seems weird
* The grab on the window happens at a large offset, so instead of the window staying in place as long as the user does not move the mouse, it makes an instant jump to the right, which seems to be the width of the screen, leading to the window being placed off-screen and unreachable if one doesn't move it back.

xfwm4 4.8.3-1ubuntu1
libgtk-3-0 3.4.2-0ubuntu0.2

$ lsb_release -rd
Description: Ubuntu 12.04 LTS
Release: 12.04