The issue has been fixed in the current version – v1.4.0 GA. Please download it from our download page and let me know if its working as expected.
When there are too many data point which can lead to label overlapping, chart tries to skip some of the labels so that there is no overlap and the chart is readable. So in most of the cases label gets skipped in order to avoid overlapping. But the above issue that Daniel reported was a genuine issue which I’ve fixed. This must have also fixed the issue in your case. Do checkout the latest version and let me know. If the issue still persists, please create a jsfiddle with your data so that I can have a look.