Rendering of y-values in bar graph unexpected with low numbers

The y-values in a bar graph are numbered unexpectedly (0,
0, 0, 1, 1, 1) if the 'Integer values' checkbox is clicked, and the value in the graph is low.

As an example, take a look at the 'Instances started by user' chart in the attached screenshot, taken from a default BPMS 6.2.0 installation after one process instance has been created.