Portage has a GTK+ 3.2.4-r1 ebuild that fail to build if CUPS is 1.6 version. This is a fix: https://bugzilla.gnome.org/show_bug.cgi?id=670373 This patches works with GTK+ 3.2.4, you need apply all 9 patches to get GTK+ work with CUPS 1.6. This patch is in GTK+ 3.4.2 release http://ftp.gnome.org/pub/gnome/sources/gtk+/3.4/gtk+-3.4.2.news And it was ported to GTK+ 2.24.
Why would you want to fix gtk+-3.2 since gtk-3.4 is stable and has the fixes ?
Because: 1). It is in portage 2). The patch was written 3). I successfuly upgraded GTK+ 3.0 to 3.2. But 3.4 version gave me some unnecessary dependencies.
gtk+-3.2 will be dropped in the near future, if gtk+-3.4 has bugs affecting you, please start reporting them