Lurking in the darkest, deepest corner of Photoshop CS6 is checkbox and a text field that control the appearance of text antialiasing.
It’s a global option, not per document, and applies gamma correction to text layers, making them look thinner or fatter, depending on the value.
Black remains black, white remains white, but the grey pixels, the antialiased areas, change in contrast and brightness.
What?!? Why would anyone ever want it to work this way?
As well as altered text antialiasing, Photoshop CS6’s default behaviour changes text layer opacity. […] This results in Blend Text Colors Using Gamma changing the antialiasing and layer opacity, which probably isn’t desireable.