failure with latest merged ACPI on virtualbox

I have a virtual machine running freebsd-current under VirtualBox (on Mac OS X).

It's been running with no issue for the last month.  Today, I updated to the
current version.

# old version (worked well)
_at_(#)FreeBSD 11.0-CURRENT #0 991d92a(master): Sat Mar 26 08:59:33 EDT 2016
FreeBSD 11.0-CURRENT #0 991d92a(master): Sat Mar 26 08:59:33 EDT 2016
    lidl_at_testvm.pix.net:/usr/obj/usr/src/sys/GENERIC

Current version, which fails:
# uname -a
FreeBSD testvm.pix.net 11.0-CURRENT FreeBSD 11.0-CURRENT #1 88a00cf(blacklist): Wed Apr 13 00:39:24 EDT 2016     lidl_at_testvm.pix.net:/usr/obj/usr/src/sys/GENERIC  amd64

It's shutdown twice (without warning), logging the following to the messages file:

Apr 28 17:08:14 testvm kernel: ACPI Error: No installed handler for fixed event - PM_Timer (0), disabling (20160422/evevent-323)
Apr 28 17:08:14 testvm kernel: ACPI Error: No installed handler for fixed event - RealTimeClock (4), disabling (20160422/evevent-323)
Apr 28 17:08:14 testvm kernel: ACPI Error: No handler or method for GPE 01, disabling event (20160422/evgpe-834)
Apr 28 17:08:14 testvm kernel: ACPI Error: No handler or method for GPE 03, disabling event (20160422/evgpe-834)
Apr 28 17:08:14 testvm kernel: ACPI Error: No handler or method for GPE 04, disabling event (20160422/evgpe-834)
Apr 28 17:08:14 testvm kernel: ACPI Error: No handler or method for GPE 05, disabling event (20160422/evgpe-834)
Apr 28 17:08:14 testvm kernel: ACPI Error: No handler or method for GPE 06, disabling event (20160422/evgpe-834)
Apr 28 17:08:14 testvm kernel: ACPI Error: No handler or method for GPE 07, disabling event (20160422/evgpe-834)
Apr 28 17:08:14 testvm kernel: .

In both cases, I was in the middle of running 'mergemaster', just after having
done a 'make installworld'.

-Kurt