Comment 34 for bug 1690719

I can confirm comment #16 now, this bug is also present in gnome on X but I didn't notice until now.

Under certain conditions this issue can completely block all GUI to the user: I just ran into a situation where I debugged an application which didn't ever return from finishing to paint/draw menus. Gnome-shell completely freeze, I could not move the mouse cursor or use my keyboard (except for switching to ttys).

You can easily reproduce this by attaching a debugger to any application and setting a breakpoint where it will be called e.g. when the user opens a menu.

So this supports Jasper St. Pierres assumption that this is blocking the mutter main thread.