Dashboard graph's items per hour's scale sometimes shifted

[chfoo]

Loading the dashboard page and not touching anything, browsing other tabs for a while, and then coming back to the page, sometimes the scale of the items per hour is shifted so that it appears there is more items per hour. Clicking one of the buttons like "all" seems to reshift the line and scale back to a correct value.

It is hard to reproduce but I see it occurring in Chromium (version 28.0.1500.71).