Now that Lenny has been released I've updated some machines and found just one flaw. There is a cvsd installation, which has been extended with an OpenSSH server. After the upgrade the server refused the connection. Enabling debugging output showed:
sshd[...]: fatal: ssh_selinux_getctxbyname: ssh_selinux_getctxbyname: security_getenforce() failed
in the log. Searching the web a bit revealed, that the CHROOT now needs a mounted /proc. Done and everything works :)