OK, I see now what you mean.
So if I save a native ArchiCAD file as IFC, an element will have a certain ID. If I now change the ID of the element, then save as IFC, the change in ID will be carried through to the IFC file.
However, if I open an IFC file in ArchiCAD, then change the ID of an element and resave it as IFC, THAT ID change will NOT be carried through to the IFC file.
I wonder if that has something to do with the fact that in the second case the ArchiCAD file was generated from an IFC file. I also wonder whether this is intentional, by design or a bug.
In any case, I cannot decide which one it is so I will just forward this to Graphisoft.
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