Mobile User Home: Vanished

Hi, First post here but am a little desperate/concerned, hence the post. I recently implemented a password policy company wide on our Open Directory. Naturally its universally hated, but is for the greater good. However, seemingly, some of our Mobile User Home users have had their account 'Vanish'. The home folder (~/User) is still there but no accounts show up in the Accounts window!!?? Any tips here/how to I manually create/get working again. BTW they can log into other computers with no issues (sans the machine with the home folder) just as 'Network Home' (with the last time they'd synced their account). I'm stumped, I realise I could drag all the stuff back onto their network home from the home folder, wipe the machine and set them back up again but this seems a little drastic! Any ideas?