Normally, when you start dasher, you see a toolbar, text box, and a canvas with an alphabet and colourful rectangles. With gtk 2.18, you see a default grey area where the canvas should be.

If you configure dasher --without-cairo, the canvas is correctly drawn on startup using gdk instead of cairo. The only file which is affected by WITH_CAIRO is

http://git.gnome.org/browse/dasher/tree/Src/Gtk2/Canvas.cpp
(and Canvas.h - CanvasExperimental isn't used by default)

So at this point, it seems that
- events are handled correctly otherwise the gdk version wouldn't work
- must be a cairo problem

But now for the surprise.

To repeat:
grab a copy of dasher e.g.,
wget http://www.inference.phy.cam.ac.uk/prlw1/dasher/dasher-cairo.tar.bz2
tar xjvf dasher-cairo.tar.bz2
cd dasher-4.10.1
./configure --without-gnome --disable-a11y --disable-nls
(to minimise the number of dependencies (toupper(a11y) = A11Y))
make
Src/dasher

If you see a grey square instead of the alphabet in colourful boxes, you see the bug.

So, the surprise is that I don't see the bug on:
- ubuntu 8.04.3 i686 with gtk 2.12.9, cairo 1.6.0, glib 2.16.6
- ubuntu 9.04 x86_64 with gtk 2.16.1, cairo 1.8.6, glib 2.20.1
- NetBSD-5.99.23/amd64 with gtk 2.16.6, cairo 1.8.8, glib 2.20.5

I do see the bug on:
- ubuntu 9.10 i686 with gtk 2.18.3, cairo 1.8.8, glib 2.22.3
- NetBSD-5.99.23/i386 with gtk 2.18.5, cairo 1.8.8, glib 2.22.3

So, it doesn't seem to be a cairo problem, as NetBSD/amd64 works with cairo 1.8.8.

It looks like a gtk 2.18 vs 2.16 problem (or glib?!) - so what changed?