When an animated sideshow is selected as the wallpaper for gnome-desktop it is not animated.
There is an upstream bug and patch available, but it has not yet been included in the mainline codebase.
GNOME bug: https://bugzilla.gnome.org/show_bug.cgi?id=601753
Sabayon Bug: http://bugs.sabayon.org/show_bug.cgi?id=1127
Created attachment 214854 [details, diff]
Created attachment 214856 [details, diff]
Patch for ebuild (against gnome-base/gnome-desktop-2.28.2)
Created attachment 214857 [details, diff]
Fixed ebuild patch
From my point of view, this patch should be applied downstream since upstream seems too busy to include it (and we can follow fedora progress with it since they are including it since some time)
Thanks Ian for reporting and the patch
Fixed in 2.28.2-r1