I've already moaned about the illogical save system the game has, now I find I'm the victim of a possible bug as well.
I had to play a good chunk of the game more than once (explanation in the link above) before I actually finished it, but both times I played through on Survivor difficulty. I just got to the end and was only awarded the "Do It Once" achievement, I should've been awarded the "Survivor" achievement as well but it never popped. I never once adjusted the difficulty in the options while playing through, I started a new game (twice) on Survivor difficulty and left it there, the game even awarded me points in the stats at the end, saying I'd completed Survivor Mode.
So what gives? Why no "Survivor" achievement? Is this a bug? Has anyone else had this problem?
This happened to me as well, I decided to play on Survivor when I first started up the game, which was a couple of hours after it was released and I've just finished it today, but no "Survivor" achievement.