usb panic

["Jeremy C. Reed" <reed%reedmedia.net@localhost>]

Sometimes, but not every time I plug in or unplug my Brother HL5150D 
printer into the USB, I get a panic.

ulpt0: detached
ulpt0: at uhub7 port 2 (addr 2) disconnected
(I am not sure if the above happened at same time or not.)

panic: kernel diagnostic assertion "c->c_magic == CALLOUT_MAGIC" failed: 
file "/usr/src/sy/kern/kern_timeout.c", line 706
fatal breakpoint trap in supervisor mode
trap type 1 code 0 rip ffffffff802590f5 cs 8 rflags 20046 cp2  
7f7ff21da000 cpl 8 rsp fffffe800631ac10
Stopped in pid 0.5 (system) at  netbsd:breakpoint+0x5:  leave
db{0}> bt
breakpoint() at netbsd:breakpoint+0x5
vpanic() at netbsd:vpanid+0x1f2
kern_assert() at netbsd:kern_assert+0x48
callout_softclock() at netbsd:callout_softclock+0x2c6
softint_dispatch() at netbsd:softint_dispatch_0xd9
DDB lost frame for netbsd:Xsoftintr+0x4f, trying 0xfffffe800631ad70
Xsoftintr() at netbsd:Xsoftintr_0x4f
--- interupt ---
0:
db{0}>

Photo at http://tx.reedmedia.net:17777/J.jpg

(By the way, when I was in X retrieving my photos off camera the system 
locked up again; I assume due to USB.)

The kernel is:
NetBSD 6.0_BETA (GENERIC) amd64
from around April 16.
dmesg is at 
http://tx.reedmedia.net:17777/dmesg.boot.txt