This bug is really puzzling. I suspect some nasty setup somewhere, or even the wrong "su" being used.
Could you please, while trying to reproduce this, use "which su" to check whether the correct su is used? It should be /bin/su If this is /bin/su, could you please check its MD5 checksum: md5sum /bin/su Should give: 49b784bf9a2e6e2a5976bc716c59a51d /bin/su The correct su binary is attached to this mail. Please try using it as well.
su
Description: Binary data
