Yep. It's happened to me as well. Based on the questions they were asking me in the interview and based on the folks who were interviewing me I got the impression I was going to be working on a certain technology very interesting to me. It took them a while to actually make the offer (2 months), by the time I started they indeed had me working on that interesting technology... but then about 2 weeks in it was like "There's been an urgent change, we now need to shift you over to working on some other [much less interesting set of tasks mostly involving writing documentation]." I figured, OK, this is just a temporary thing and after the urgent project blows over I'll get back to what they wanted me to work on originally. I'd often ask when I was getting back to work on the original project and they'd always hem and haw. Eventually it became clear that it was a bait&switch.