Originally posted by keanex is it possible for this to get worse over time? If so I'll return it for a less out of adjustment lens.
I've no idea about that, seems unlikely but who knows. I do know that I had to AF tune almost all of my lenses on the k-5. On the k-3 I went through the testing process and finally just gave up, out of 10 tested only one had any noticeable error and it was not quite -1, so I just left it alone.
As to returning it. If I were you I would conduct the test again, in different light preferably daylight. If the results are the same, then yeah I would return it. This does not mean the lens is bad, just that it is 'off' in a direction that makes it not work with your particular camera. The way I understand it is if say the lens is +6 and the camera is -4 then an adjustment of +2 makes it right. But if the lens is +6 and the camera is +5 then you need +11 to make it right, which you cannot do.
You don't say what camera but I believe the k-5 had a particular issue with front focusing in incandescent (yellow) light. So if you have a k-5 you might want to read up on that issue. One of the improvements in the AF of the k-3 was to adjust for this.