dev-python/gnome-python-extras depends on both >=dev-python/gnome-python-desktop-2.14.0 and >=dev-python/gnome-python-extras-2.12, however, gnome-python-desktop-2.14.0 blocks <dev-python/gnome-python-extras-2.13. The end result is that, when updating world, it fails because of that conflict. However, after dev-python/gnome-python-extras is unmerged, with the next update it's pulled in again, courtesy of deskbar-applet.
you need to unmask gnome-python-extras so you get > 2.13.
Hm, my naive approach to a solution would be to have deskbar-applet depend on >=dev-python/gnome-python-extras-2.14 ...
Opened bug 132596 in relation to this bug