classes and subclasses and inheritance

I am slowly figuring things out, but have gotten stuck.  Maybe this is something basic?

I am using DrGeoII.  I have defined a DrGPolygoneMorph which is a subclass of DrGPolylineMorph then a subclass of PolygonMorph.   I am trying to flip this object and using the method flipHAroundX:nil 

This works when I create a PolygonMorph, but doesn't seem to do anything to my DrGPolygoneMorph.  Doesn't inheritance mean is should work identically?

david