FreeBSD 8.0-CUR: /usr/ports/x11/linux-f8-xorg-libs won't install although emulators/linux_base-f8 is already installed

[O. Hartmann]

Before filing a PR I will ask for hints for a problem I revealed when I 
wanted installing usr/ports/x11/linux-f8-xorg-libs on a FreeBSD 
8.0-CURRENT/amd64 box (most recent build_world, ports tree up to date).
I receive this error:

===>  linux-f8-xorg-libs-7.3 the port should be used with linux_base-f8, 
please read /usr/ports/UPDATING.
*** Error code 1

Stop in /usr/ports/x11/linux-f8-xorg-libs.


Package /usr/ports/emulators/linux_base-f8 is already installed, up to 
date and Linux kernel module is also running and showing up when doing 
kldstat adjacent with linprocfs and linsysfs.

What's wrong?

Oliver