IFC import/export is still problematic. Unfortunately very often elements, that exported from ArchiCAD to Revit and vice versa are becoming unchangeable, that is, of course, very strange - because the whole idea of IFC - is to exchange information between AEC software without loosing any of parameters.
Very possible, that this is how IFC import works - this way Autodesk is forcing their users to stick with Autodesk product. Even the new plug-in for ArchiCAD, that exports RVT file, creating static elements, that impossible to modify in Revit.
I imagine, that if existed some sort of international court, that would force AEC software venders to provide proper data exchange (as regulation against monopoly) - this problem would be fixed immediately. Without that, I assume, the problem will present for long period of time.