Urg. I didn't realize Linux behaved so oddly. Yet another
reason not to worship Linux (don't get me wrong, I make
my money as a "Linux specialist"). Not only is Linux behaviour
not portable, the entire chroot concept isn't. chroot is not
part of the POSIX standard.
Not that I am arguing in favour of Linux worship but the chroot man page does say that the linux implementation conforms to a number of standards "CONFORMING TO SVr4, SVID, 4.4BSD, X/OPEN. This function is not part of POSIX.1." and the OpenBSD chroot man page also states that "There are ways for a root process to escape from the chroot jail". Without actually comparing code it is impossible to say one way or another but on the surface it would appear that the Linux implementation is not that "odd".
-- Do not seek to follow in the footsteps of the wise. Seek what they sought. -Basho