If kde-base/kde is installed and then then what it installs, kde-base/kdebase, etc. are removed allowing kde-base/kde-meta to be installed, emerge -uD will cause emerge to try to install all of its dependencies again. These will now be blocked by the kde-base/kde*-meta packages. Reproducible: Always
Well, was probably due someone stumbled about it. Thanks Dirk, fixed for 3.5.6.