Looking around at what the GTK+2 -> GTK+3 transition involves, I found all the things marked “deprecated” in GTK+ API have been removed to clean it up; fine unless appliactions use the deprecated features. On the GNOME3 Developer site there’s some advice info on porting GTK+2 -> GTK+3 with links to portability guides - DevGnomeOrg/Gnome3PortingGuide - GNOME Live! eg) Migrating from GTK+ 2.x to GTK+ 3. Might help targetted testing or at least help explain issues.
I recommend, if one has nVidia hardware, to apply the ‘nouveau’ graphic driver fix first. GTK3, when it works, looks nicer on LXDE than the older GTK2 and having nouveau instead of nv or fbdev makes a difference. But LXDE w/GTK3 is still rough around the edges and the theme is not working yet on all nominal LXDE desktop apps.
I ended up also enabling the debug repos to help (I had to be prodded by anubsig1 to do so - I can be slow with adding new repos) in order to run a back trace … first time I’ve done so in years (again, anubsig1 had to walk me through it on the IRC chat channel freenode #opensuse-lxde.
# then press "r"
# it then complained with "try with zypper in -c" bla bla bla"
# which I ended up installing in another terminal