Documentation implies that QHXYModelMapper default for columnCount is -1, which will limit the columnCount to the value from the model. In practice, columnCount needs to be set explicitly, or QHXYModelMapper will try and map data from invalid columns above the number in the model. Either the documentation or the implementation should be changed so they are in agreement.

Relevant forum thread:
https://forum.qt.io/topic/72832/crash-when-assigning-proxy-model-to-chartview-but-not-tableview/4