IFC hierarchy for floor sub-elements

I have found what I think is a bug introduced after 21.1.0.0 for IFC4 export (and I think a bit earlier for IFC2x3 export) and it relates to exporting floors that have had their subelements modified in Revit (all versions).

The image below shows the same model exported using two different versions of the IFC exporter (21.1.0.0 and 21.4.2.0). The later version shows the triangulated sub-elements as being separate slabs underneath the main slab element (which is no longer being exported as an IfcSlab).

This bug is rendering our IFC-models unusable and is preventing us from upgrading beyond version 21.1.0.0.
Any assistance would be greatly appreciated!
I'm happy to provide any further information to help explain the problem if required.


In version 21.1.0.0 the entire floor was included correctly in the IfcSlab:

But in any later versions each triangulated volume was exported separately as an unwanted sub-element.

And thanks for all your great work so far!

The report concerns IFC4 and IFC2x3 export from Revit, comparing exporter versions 21.1.0.0 and 21.4.2.0, but names no source file or test. Begin by reproducing the two exports with a floor containing modified subelements and compare their IFC hierarchies. Done means the main floor remains an IfcSlab and triangulated subelements are no longer exported as unwanted separate slabs.

Written by the indexing model from the issue text.