As reported by others, downgrading to libtirpc1/0.2.2-5 and libc6/2.19-1 (and restarting rpcbind, nfs-common, and nfs-kernel-server) makes the issue vanish. I think this bug is grave, since it prevents NFS from working.
Everything works with libtirpc1/0.2.3-2 and libc6/2.19-4 Thank you