The following warnings appear in applications with Gtk

Gtk-WARNING **: xxx: Theme directory 16x16/actions of theme openSUSE-Xfce has
no size field
Gtk-WARNING **: xxx: Theme directory 22x22/actions of theme openSUSE-Xfce has
no size field
Gtk-WARNING **: xxx: Theme directory 24x24/actions of theme openSUSE-Xfce has
no size field
Gtk-WARNING **: xxx: Theme directory 32x32/actions of theme openSUSE-Xfce has
no size field
Gtk-WARNING **: xxx: Theme directory 48x48/actions of theme openSUSE-Xfce has
no size field

Adding the missing entries in /usr/share/icons/openSUSE-Xfce/index.theme like

[16x16/actions]
Context=Actions
Size=16
Type=Fixed

shut up the warnings, at least.