If I enter "emerge -u -p world" not all outdated packages are shown. It seems to me that only the basic system ones will occure. I.e., if I enter "emerge -p -u gnome" or "emerge -p -u mplayer" then these packages are outdated and marked for an update. Nevertheless they do NOT appear after having typed "emerge -p -u world".
*** This bug has been marked as a duplicate of 5872 ***