As far as I know when you install x11-themes/gnome-themes-2.8.1 it also install the smooth engine as well as several other engines. However, if you emerge x11-themes/gnome-themes-2.8.1 and then emerge x11-themes/gtk-engines-smooth no block shows up and you are allowed to go through with the ebuild. After you are done, portage does pick up the problem. Reproducible: Always Steps to Reproduce: 1. 2. 3.
Seems like there is another problem with the smooth engine or gtk engines in general. When you emerge gnome-extra-themes it should also install the gtk engines need in order to run the themes included ( smooth is one of the engines). As far as I can tell it does install them and gnome uses the engine provided that you use a theme that utilizes it. However, if another gtk application tries to use the engine it seems to not be able to find the files. I am not sure what the problem there is but if you manually install the engine in /usr (not through portage) all the problems disapear. As far as I can tell there is a problem with the ebuild. If I were the maintainer I would probably remove the engines from the gnome-extra-themes ebuild and also replace the blocks in the ebuild for the engines with depends (but that's just me).
Fixed in portage, thanks for info and help.
