debug.debugger_on_panic = 0 yet still entering db

i'd like to get a bt from a panic which occurs after doing `acpiconf -s 3`.
since i'm using a usb keyboard (which doesn't work in db) i've set
debug.debugger_on_panic = 0 ("options KDB_UNATTENDED" in kernel).

yet when the panic occurs freebsd still enters the debugger!

i also get another panic which is virtualbox related, but when the virtualbox
related panic occurs the core gets dumped and freebsd reboots as it should do.

since i cannot use my usb keyboard when the acpi panic occurs i don't know
what kind of panic this is, but i think it saw the term "spinlock".

i'm running r194284. this is the output of `sysctl -a|grep panic`:

kern.sync_on_panic: 0
debug.ddb.textdump.do_panic: 1
debug.trace_on_panic: 1
debug.debugger_on_panic: 0
debug.kdb.panic: 0
machdep.enable_panic_key: 0
machdep.panic_on_nmi: 1

cheers.