kernel crash on destroy a cloned wireless interface

hi,

i have an integrated wireless interface and an usb one. i wanted to  
switch between them to do some tests and each time i try "ifconfig  
wlan0 destroy" i get a kernel panic.
here is the kernel dump after one of the crashes.

http://www.itavy.com/freebsd/dump-200812201556.tar.bz2

-- 
Octavian