Parameter mapping

I have some troubles with parameter mapping to FireRating in Ifc.
I use Revit 2019.2.1 with exporter 19.3.
I have my own ParameterMappingTable.txt to set a Dutch named Firerating parameter to FireRating in IFC. I do this in the Pset_WallCommon. Revit also has its own Fire Rating parameter but this is not sufficient for us. I thought that a ParameterMappingTable would override the standard parameter mapping from the IFC exporter, but this does not happen. Instead it just adds an extra value in the FireRating parameter in the Pset_WallCommon.

Start by reproducing the reported Revit 2019.2.1 export with exporter 19.3 and the custom ParameterMappingTable.txt, focusing on mapping a Dutch Firerating parameter into Pset_WallCommon. Trace how the custom mapping and Revit's built-in Fire Rating value are combined; done means the custom mapping overrides the standard value instead of adding a second FireRating value.

Written by the indexing model from the issue text.