In [attachment:z-index.png] the most important curve (the one with the most visits) is sometimes hidden by a less important curve.
Curves should be painted in reverse order of importance.
In pChart, it is possible to specify in which order the curves are drawned. However, this also changes the order the legend is written. This means the most important curve would have it's name drawn last in the legend.
It would be nice, but because of the bug you mention I assume it's non trivial, so moving to feature requests