GTK3 resize grip freezes the window manager

[Jeremy Henty <onepoint starurchin org>]

This may not  be a bug in Gtk3  but it does seem connected  to Gtk3 so
maybe you can help.

If I run any Gtk3 application  and click the resize grip at the bottom
right then my  desktop instantly freezes - it does  not respond to any
key or  mouse events.  There is no  such problem with termit  - a Gtk2
application that  has a resize  grip on the  status bar at  the bottom
right.

This happens  with my  standard icewm desktop  and also with  twm.  (I
tried the experiment with no window manager at all, just the Gtk3 app,
but then the mouse disappeared.  No idea why, maybe X needs requires a
window manager to be running these days?)

During the  freeze nothing seems  to be happening.  All  the processes
are  in sleep  (ie.   there is  an 'S'  in  the 'S'  column in  htop).
Interestingly, the time applet in  the icewm status bar still updates.
If I kill the Gtk3 app then everything recovers.

How can I investigate this further?

(Linux 2.6.37, Xorg 7.5, icewm 1.3.7) 

Regards,

Jeremy Henty