Fail to remount root on nfsroot install

Binary package hint: upstart

Description: Ubuntu 10.04 LTS
Release: 10.04

After upgrade from Karmic to Lucid on an nfsroot install, reboot failed.
The initramfs loaded properly, but after switching to init, the screen switched to the framebuffer and hung with a message about portmap exit status 1

I then switched the boot to use init=/bin/bash
I see that the root filesystem is mounted correctly, read-only
I run exec /sbin/init
and get hung with a message about plymouth-splash exiting status 2

if I manually remount the filesystem rw, I can then exec /sbin/init and the system starts properly

In the end, I added 'rw' to the boot parameters such that root is mounted rw by initramfs (and removed he init= parameter), then boot works properly.
As it worked fine in Karmic without this, it seems like something in init is preventing the filesystem from remounting read-write

My fstab file:
proc /proc proc defaults 0 0
/dev/nfs / nfs rw,nolock 0 0
none /tmp tmpfs defaults 0 0
none /var/run tmpfs defaults 0 0
none /var/lock tmpfs defaults 0 0
none /var/tmp tmpfs defaults 0 0