Help - disassociating a project from a client company

Help - disassociating a project from a client company

I mistakenly associated a project to two companies and I just can't get rid of one of them. I've tried :

removing via CRM interface
removing via Zoho Projects > Settings > Manage Users > Client Users and ensuring that the project is unticked in All Projects/Working Projects - but saving it never seems to "stick"

But this one project always shows both companies. 
I don't want to have to delete the companies and recreate/reassociate everything else