They've been doing it for years ... a good friend of mine resigned his command with a Gulf major back in 2008 on the promise of a European base with China Southern ... worked his 3 months notice ... literally the day before he was due to arrive in China to start his training he was informed by email that the European base was no longer available and he would be China based.
They just lie, because they know once you've done your notice at your previous employer you're screwed and you can't go back