NTOS: Timer fired even though it was canceled

[Eitan Adler]

Running freeBSD 8.0-RELEASE I got
NTOS: timer 0xc4817a08 timer fired even though canceled

from
http://fxr.watson.org/fxr/source/compat/ndis/subr_ntoskrnl.c?v=FREEBSD8

       /*
        * This should never happen, but complain
        * if it does.
        */

        if (timer->k_header.dh_inserted == FALSE) {
               mtx_unlock(&ntoskrnl_dispatchlock);
            printf("NTOS: timer %p fired even though "
                    "it was canceled\n", timer);
                return;
        }


What might have caused this and how could I fix it?