[gentoo-amd64] Portage Fails To Find Updates

[Frank Peters <frank.peters@comcast.net>]

Today, doing an "emerge -pvDu world" I get the report that no packages
need to be updated.

But while checking the status of another package, I happen to execute
"emerge -pv rpm2targz."  This then reports that the package rpm2targz
needs to be updated.

Why didn't the "emerge -pvDu world" tell me about this?

Further checking reveals that all packages that are installed on my
machine are contained in the /var/db/pkg directory.  However, the "world"
file, which is located at /var/lib/portage/world, should contain the same
listing but it does not.  I notice that some packages in /var/db/pkg
are not listed in /var/lib/portage/world.

Actually, the "world" file has 257 entries, while the "/var/lib/portage/world"
directory contains 414 packages.

Why has portage failed to add all packages to the "world" file?
Have I been doing something wrong?

In any case, I can rebuild the world file manually to accurately
reflect the state my system, but, based upon this current observation,
portage may fail to keep it accurate in the future.

What is going on here?

Frank Peters