Can't read 2 Input axis at once?

I've assigned left control as the positive to an input axis and 'a' + 'd' to the positive and negative of another axis (called Sideways).

I print out the value of Input.GetAxis("Sideways") every frame. If I hold left control and tap 'a' or 'd', the output stays as 0. If I release left control and press 'a' or 'd', the output value changes as expected.

Is this a bug? I am able to read my Forward axis ('w' + 's') at the same time as pressing left control just fine. I am using a slightly older version of Unity (3.5.2f2).