Comment 16 for bug 900972

the kernel's devpts newinstance support is more limited than I remembered. When you do 'mount -t devpts -o newinstance devpts /dev/pts; mount -t devpts devpts2 /mnt', then the second devpts mount under /mnt will be the global kernel instance, not the last instance you mounted with newinstance.

I'm not sure yet why precise isn't exhibiting this behavior. It would seem to be a neat trick, and whatever is stopping this from happening through the fstab entry in precise, in general the guest cannot be stopped from doing this (without LSM or user namespace interference).