gentoo “broken” world file

Yesterday, I did an “eix xpad” and I saw that there were newer versions than I had installed…That was weird because I daily do my “emerge -uDav world”. That was not the first time though such a thing had happened. So I opened my “/var/lib/portage/world” file and started checking for some of my packages that should be in there, like gimp, k3b, etc. There were just not there.
What I did was copy the world file to the root dir and then “regenworld”. Magically around 40(!!) new packages appeared inside the world file.
“emerge -uDav world” gave me aroung 20 packages to upgrade. Then I did an “revdep-rebuild” and my system is rocking again 🙂
I still don’t have an explanation of why did this happen…why weren’t these packages inside the world file…possibly broken emerge commands…but why ?