Legend contents wrong when using Contour Plots amongst others in charts/graphs

(Using Gnumeric 1.12.44)

I was curious whether I could draw "live" calculated rectangles on a graph pane. While nearly impossible in LibreOffice, Gnumeric was able to approach that technique: with contour panes (although you can't choose the color stepping distances or the actual colors themselves there unfortunately - this is feature request #405).

But after having plotted the rectangle (amongst other plots), I discovered the broken legend:

Show colors in legend	Show in legend	Result
Yes for all plots	Yes for the series of all plots	Acceptable (per plot: the series name and 9 color definitions in legend - color definitions are overkill, they could be fewer)
No for all plots	Yes for all plots	Fail: only first series name and one plot color in legend
No for all plots	Yes for first plot	Acceptable (only first series name in legend - the line color of the series will not match the graph in case the contour shows fully equal values so no color difference happens so no line will be painted)
Yes for first plot	Yes for first plot	Fail (first series name and only eight out of the nine colors show up in legend)
(more	combinations)	There are several more combinations which lead to errors.

Following file illustrates the case "No colors in legend, all series names in legend": ContourPlotLegend-Bug.gnumeric.xml