I've recently found gtk+-smoothscroll patch Gentoo is using to break GtkSpinButton behaviour. Details and fixed version of the patch at http://bugs.gnome.org/show_bug.cgi?id=103811
added the fixed patch to 2.4.13-r1, thnx You've been working on this patch, so maybe you got time to crack #61342 as well ?
Why not, I'll take a look, if time permits.
I think the bug is important enough to have the revised patch also in stable gtk+ (~=2.4.9). One must check whether it applies cleanly, though.