Cannot find Root filesystem. Bug in intramfs/init detected. Dropping to a shell. Good luck!

[Joshua C.]

As the subject says I get the following error with F11 Alpha: "Cannot
find Root filesystem. Bug in intramfs/init detected. Dropping to a
shell. Good luck!" I tried a custom livecd with rawhide as of
23.02.2009 and got the same behaviour. The plymouth starts and the
modesetting works, when using debug at startup the kernel boots and
detects most of my hardware and then comes this error message.

I then made a custom F10 livecd with the 2.6.29.rc kernel and got the
same error. I changed the kernel to 2.6.28 and rebuild the livecd with
same components as before (they were cached at the first build) and
everything worked just fine. This makes me think that the error comes
from the kernel itself, but there are no kernel-oops at startup and
when building the livecd the kernel installs without errors.

Has anyone experienced this? Any ideas? Should I file a bug report?
Against which package?