When PHPlot calculates defaults for X and Y tick label and data label positions, it stores those into the object and then uses them as if they were set directly. This can produce unexpected results with multiple plots.
Original bug report: [bugs:#164]. Other cases there have been fixed. The label positions are more complex and still not fixed.
Example: Plot 1 has X labels in the data array, so by default PHPlot turns on X data labels and turns off X tick labels. Plot 2 has no X labels in the data array, but PHPlot continues to keep X data labels on and X tick labels off, so you get no labels along the X axis for plot 2.