Aha! I was finally able to duplicate this problem!
This is a known (fixed) bug that has to do with the way that we are determining which units and values to use for the horizontal axis. This bug is hyper-sensitive to the width of the chart which is why I was unable to duplicate it until I used Drew's 15em trick.
As a work-around, I suggest that you change the version number in the google.load statement from "1" to "1.1". This will get you our about-to-be-shipped version. In the meantime, I'll verify that this is indeed the problem, and see about cherry-picking the fix.
Let me know if you continue to have problems, and keep an eye out for the release announcement.
George