My last employer did this. Not so much the exact scenario, but they constantly assured us they were fully committed for the long-term to our satellite office that they opened. They went out of their way to reiterate this quite regularly and put a good of effort into it. Until one day they showed up and shut down the entire office.
I just don't understand why. Who treats people like that? It's not like these decisions just suddenly pop up out of the blue one morning and a decision to fire people has to be made immediately. Clearly companies have to mull over this type of stuff for quite some time. I don't understand why you reassure people like that only to completely up-end their lives. Knowing that B&N pulled this crap, I'll definitely be avoiding them moving forward.
So moral of the story is, when I company has to start assuring you that you most definitely won't be let go any time soon, it's a pretty good indicator that it'll be happening very soon.