Then you probably just dropped under it's minimum supply voltage 
1V is pretty low and most can't do that.
Also, 1V to 12V gives you a ratio of 12. The current on the input is 12 times higher then the input, not including the efficiency. Let's say that's 80% (just random, it's probably way lower) you already have a current that's 12 / 0,8 = 15 times higher then the output current... That's pretty extreme.