Currently I am running solo with two different characters in two different worlds, one which pre-dated 1.0 and one created new. I reached the Survivor achievement with one character, and it showed up on my list of Steam achievements and on that character's achievements. Yesterday, the other character got the Survivor achievement. This morning, the Steam achievement is still there, but both characters' survival achievements are gone. The Player Statistics for both of them show that they survived a maximum of 3 days, with their current "streak" at 2 days.