shared lib issue in /usr/obj?

Hi

$ sudo rm -rf /usr/obj/*
rm: /usr/obj/usr/local/freebsd8/src/lib32/usr/lib32/libc.so.7: Operation 
not permitted
rm: /usr/obj/usr/local/freebsd8/src/lib32/usr/lib32/libcrypt.so.5: 
Operation not permitted
rm: /usr/obj/usr/local/freebsd8/src/lib32/usr/lib32/libthr.so.3: 
Operation not permitted
rm: /usr/obj/usr/local/freebsd8/src/lib32/usr/lib32/librt.so.1: 
Operation not permitted
rm: /usr/obj/usr/local/freebsd8/src/lib32/usr/lib32: Directory not empty
rm: /usr/obj/usr/local/freebsd8/src/lib32/usr: Directory not empty
rm: /usr/obj/usr/local/freebsd8/src/lib32: Directory not empty
rm: /usr/obj/usr/local/freebsd8/src: Directory not empty
rm: /usr/obj/usr/local/freebsd8: Directory not empty
rm: /usr/obj/usr/local: Directory not empty
rm: /usr/obj/usr: Directory not empty
$ uname -a
FreeBSD marina 8.1-STABLE FreeBSD 8.1-STABLE #1: Sun Nov 21 00:48:28 EST 
2010     root_at_:/usbj/usr/local/freebsd8/src/sys/GENERIC.ndebug  amd64

Is this a corrupted obj directory ? If so, why should theses libs have 
the schg flag enabled?

Thx,

Etienne

$ sudo ls -lao /usr/obj/usr/local/freebsd8/src/lib32/usr/lib32/
total 2520
drwxr-xr-x  2 root  wheel  -      12288 Dec  9 07:24 .
drwxr-xr-x  3 root  wheel  -        512 Dec  9 07:25 ..
-r--r--r--  1 root  wheel  schg 1128116 Nov 21 02:15 libc.so.7
-r--r--r--  1 root  wheel  schg   32060 Nov 21 02:18 libcrypt.so.5
-r--r--r--  1 root  wheel  schg   16444 Nov 21 02:27 librt.so.1
-r--r--r--  1 root  wheel  schg   76668 Nov 21 02:19 libthr.so.3