A difference in MoI is that it's import and export work a bit differently... With PunchCad, you cant "save" a STEP file.. You just export one. In MoI, if you are set to mm and "Import your file" it will have correct scale. If you "Open" it, it will default at inches...

Delcam Powershape handles this file the same way... I dont think that "MM" is defined in the file correctly. It seems to be just "Units" with a scale factor.