Thanks StaleKangaroo85 bug is verified. Let me check to see where exactly is the bug.

Two points
Notice that x_labels should be the size of the histogram It seems that you have to pass the labels as well (otherwise you get the trace-0), so if you add labels=['random histogram'] and labels=['random histogram2'] , you'll get the correct legend.Anyhow I'll make sure we also fix it in code so it is automatically labels are [series] if not specified, thanks!