Thanks for your comment! After doing a bit more diving into the original AC 9 code for that object, I can possibly shed some more light on the issue. First of all, it is not surprising that the behaviour kept changing for a number of releases: the AC...

Well, another 7 years have passed, and I have no idea whether any progress has been made on this. I am trying to use a standing-seams roof cover on Archicad 9. (Yes! In our retirement we can't fork out for a subscription any more, so we keep this one...