Interesting, seems it can work sometimes. I tried it on another one of our files and it did work! However I rechecked the file i am having problems with and it is definately not working
I think i have worked out that if you rotate the drawing in the layout, that is when the co-ordinates will not match up in AutoCAD model space and ArchiCAD floor plan. Can you try using the same drawing but rotate the drawing in the layout.
Otherwise i can only think it is something to do with the drawing being far from the origin.