Hi Bjorn,
This is a bug I reported in 15 and 16. The IFC model viewed in an IFC viewer such as Solibri shows the windows retained their vert. position. It is only when the IFC file is opened up back in Archicad that the windows are shifting their position vertically.
Check with your engineers whether the model IFC imported OK into their program; it may have.
In the meantime check your model in an IFC viewer. My screenshot shows
Solibri Model Viewer , great for mac. Other free viewers but PC only are
DDS CAD and
Tekla BIMsight.
Erika
Architect, Consultant
MacBook Pro Retina, 15-inch Yosemite 2.8 GHz Intel Core i7 16 GB 1600 MHz DDR3
Mac OSX 10.11.1
AC5-18
Onuma System
"Implementing Successful Building Information Modeling"