ifconfig can't remove aliases

[oHmEr]

hello,

i have a problem with ifconfig: it refuses to delete an ipv6 alias for an
incomprehensible reason. here's what i'm doing :

$ uname -a
FreeBSD homer.cload.net 6.0-RELEASE FreeBSD 6.0-RELEASE #4: Sun Nov 27
19:01:40 CET 2005     root at homer.cload.net:/usr/obj/usr/src/sys/HOMER 
i386
$ ifconfig dc0
dc0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
        options=8<VLAN_MTU>
        inet6 fe80::248:54ff:fe12:76fb%dc0 prefixlen 64 scopeid 0x1
        inet6 2001:7a8:b138::1 prefixlen 64
        inet 192.168.2.253 netmask 0xffffff00 broadcast 192.168.2.255
        inet6 2001:7a8:b138:caca:caca:caca:caca:1 prefixlen 64
        inet6 2001:7a8:b138::caca:1 prefixlen 48
        ether 00:48:54:12:76:fb
        media: Ethernet autoselect (100baseTX <full-duplex>)
        status: active
$ sudo ifconfig dc0 inet6 -alias 2001:7a8:b138::1
ifconfig: ioctl (SIOCDIFADDR): Can't assign requested address

other ipv6 addresses can't be removed too. is it a bug ? what can cause
this error ?

-- 
Matthieu Michaud - EPITA 2007