I still can't reproduce this on 3.6.8. one thing to note as well... in your screenshot the width is 413. In the scene you attached, the width is 414 (or perhaps I changed it to that after moving the label, not sure). You're using some font I don't have, and I just see "Arial" in the scene you attached. I also use Windows here -- 8.1 to be exact.
Make sure that you're using a width/height that's dividable by 2. Your label is centered. If you don't do this, then you're effectively trying to align to half-pixels instead of to pixels.