Qt for Python (PySide/Shiboken)

It seems that the pyi-type attribute of the modify-argument tag eats the argument default value. I've dug to sources/shiboken6/ApiExtractor/typesystemparser.cpp and the parseModifyArgument function there. However, when I comment the argumentModification.setPyiType(pyiType); line out and re-run python setup.py build --reuse-build --module-subset=Core, I keep seeing that the types are replaced as before. Is the CPP file a wrong place?