Revit duplicates a lot of fitting types

Not sure if this is related to #510 but on Revit 2021 (sorry, I know it's annoying with bugreports of older versions but such is the reality of enterprise software adoption in large companies) but I'm seeing regular (non-fabrication) pipe fittings having lots of duplicate types. For example, a single pipe fitting (i.e. one Revit Element ID) is coming through as 68 separate IfcPipeFittingTypes. In another case a single pipe fitting is coming through as 1,226 (!!! yes!) separate types. It seems specific to fittings, so segments are not affected.

Start by reproducing the issue in Revit 2021 with regular pipe fittings and compare the generated IFC types for one Revit Element ID. Investigate why fittings produce duplicate IfcPipeFittingTypes while pipe segments do not; done means duplicate fitting types are eliminated without affecting segments.

Written by the indexing model from the issue text.