In some situations JFreeChart clips the labels of (vertical, range-) axis.
This depends on the used font-size, the configured padding for the chart and of course the tick untis.
Attached is a self-contained demo that demonstrates the problem with JFreeChart 1.0.14.
See the comments inside the class to work around the problem or make it more obvious.
The bug #925902 may be related to this one. It describles a similar problem but with horizontal clipping of axis labels.