Panic at shutdown

Hi,

sometimes I have the panic in the photo at shutdown:

http://imgur.com/mXrgFLp

Unfortunately this happens randomly.

I am running:

$ uname -a

FreeBSD ativ 11.0-CURRENT FreeBSD 11.0-CURRENT #3 r291160M: Sun Nov 22
17:10:38 CET 2015     root_at_ativ:/usr/obj/usr/src/sys/GENERIC  amd64

Regards,

Maurizio