Due to the low amount of bugs received on our GNOME 2.18 release in testing, this version moves to extra quite quickly.
Some problematic packages stay in testing until there's a proper fix to get them working correctly as the old versions did.
Some other packages will force us to redesign their PKGBUILD scripts, which takes some time. These haven't been updated yet while the previous version continues to work fine.
For those who weren't using it from testing yet: Have fun with GNOME 2.18!