I was testing the new auto legend functionality and became confused when trying to plot an OGR/GMT format polygon file (i.e. with # @VGMT1.0 @GPOLYGON in the header). This entry was not added to the legend. When I removed the header, it showed up.

Maybe specify in the docs that auto legend only works when dealing with lines/points (if that is the case)? Or trick GMT by malforming the OGR/GMT file header.