Your interpretation is correct I think. There isn’t any magic here the part is simply not valid. An additional issue is the the OuterCurve of the IfcArbitraryClosedProfileDef is not closed, as it is a line segment. I think this is pretty typical for the state we are in with IFC, we don’t have great tooling openly available to automatically validate the rules and constraints. On the other hand we have some rather permissive viewers that try to accommodate invalid files (sometimes on purpose by implementing work-arounds, sometimes by accident when strictly following the rule is actually more work to implement). So quite a few of these issues go undetected. Tagging @angel.velez or maybe better report here https://sourceforge.net/projects/ifcexporter/ with some steps to reproduce.
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