Upgrading userland => kernel with same module API version does not boot

[Joachim König <him%online.de@localhost>]

Hello,

I made a build yesterday and as the kernel module API version
did not change (5.99.11) I only installed userland without
building and installing a new kernel. Installing userland also
installed (overwrote) the kernel modules in /stand.

After booting, the kernel could not mount root, it does not
seem to have/find the ffs module but does not explain why.
Booting with "-a" it only offers "generic" for the root fs type.

Rebuilding my kernel and booting that, the system boots as before.
My old kernel was from  2009-05-04, e.g. beginning of mai,
and UPDATING has no remarks after that date.

Is this behaviour expected? Do I have to install a new kernel
every time I want to install an updated userland even if the
kernel module API did not change?

Joachim