gnome-python-extras-2.12.0.ebuild depends on: =gnome-extra/libgtkhtml-2.6* Though it compiles with libgtkhtml-3.8.1 fine, like the rest of gnome-2.12
libgtkhtml-2.6 and libgtkhtml-3.8.1 are two seperate branches of a html rendering library based on gtk. libgtkhtml-3.* is maintained by the evolution team for evolution while 2.* is used by the rest of the desktop. This isn't a bug