Really late reply for me, but I just suffered the pain of this problem as well.
What fixed it for me (after trying the Axis label settings and intervals from those screens, none of which worked!) was select the Horizontal Axis, then when you can see all the properties find Labels, and change LabelInterval to 1.
For some reason when I set this from the pop up properties screens it either never 'stuck' or it changes a slightly different value that didn't fix my issue.