geli boot issues with recent kernels

My kernel and / are on ada0s1a (UFS) while the rest of the system
is on a ZFS pool on ada0s1d.eli, attached on boot.

Since a few days ago, booting no longer works reliably for me.
Every now and then the system hangs at the time when I'd normaly
provide the passphrase.

The last times this happened I was in a hurry, so I'm not entirely
sure if the prompt for the passphrase is even shown (on my system
it's always buried in USB messages anyway).

Sometimes keyboard input is ignored completely, sometimes I can
still use shift lock or scroll through the kernel messages.

When this happened the first time, rebooting the system solved
the problem. By "rebooting" I mean shutting down the system by
keeping the power button pressed and then powering the system
on again. When the system hangs, it doesn't seem to react to
the ACPI event that is generated by pressing the power button
shortly.

Today I rebooted the system three times in a row without getting
it to work so I finally unloaded geom_eli from the loader prompt,
booted to single-user mode and attached the geli provider from
there. When I booted a few hours later with the same kernel it
worked right away.

I think I experienced the problem the first time with
a kernel from last Wednesday, currently I'm using:
FreeBSD 9.0-CURRENT Fri Sep 17 18:25:39 CEST 2010 amd64

It definitively didn't happen with a kernel from last Saturday,
but then again I seldomly boot the system more than once a day
and the problem doesn't always show.

I enabled boot_verbose="-v" and kern.geom.eli.visible_passphrase=1
and thus expect to be able to provide a more detailed problem
description the next time this happens.

Has anyone else seen this?

Fabian