I recently had a project that was a collaboration between our firm and another architectural firm using Autocad. We drew the reflected ceiling plans using Archicad and used fills with a user defined origin for the suspended ceiling grid. Now during construction the contractor asked for a DWG file for the sprinkler contractor to use in laying out the head locations. I agreed and proceeded to open the file and publish a dwg - an easy and quick procedure. Anyway when the file was opened the grid had shifted and I had the grid running through my light fixtures. I looked like an idiot. I had also published a PDF from our plotmaker file, so at least I could show that it was drawn correctly.
I remember that this was a problem in the past, but I thought this had been corrected. I'm sure that the problem has something to do with the sharing of the files from AutoCad, but at this late date I cannot trackdown how it was drawn. It's possible that the fills originally came from the AutoCad using firm and were not originally Archicad.