Detaching USB stick crashes BETA4/BETA5

Hi,

i have a problem with my USB stick on 5.3 BETA4 and BETA5 which did not exist 
in 5.2.1. Whenever i detach my USB stick FreeBSD crashes. I see the 
following:

uhub3: at uhub1 port1 (addr 2) disconnected
(da0:umass-sim0:0:0:0): lost device
(da0:umass-sim0:0:0:0): removing device entry
umass0: detached
(null): at uhub3 port1 (addr3) disconnected


Fatal trap 12: page fault while in kernel mode
fault virtual address     = 0x400
fault code                  = supervisor read, page not present
instruction pointer       = 0x8:0xc04d5854
stack pointer              = 0x10:0xcc726bd4
frame pointer              = 0x10:0xcc726bd4
code segment            = base 0x0, limit 0xfffff, type 0x1b
                                = DPL 0, pres 1, def32 1, gran 1
processor eflags         = interrupt enabled, resume, IOPL = 0
current process          = 40 (usb1)
trap number               = 12
panic: page fault


This happens on an IBM X24 Laptop and a Fujitsu-Siemens Scenic 400 Desktop.

Regards,
 Lutz