For some reason, there was a huge offset on the home-position. I donīt know if it was bad GPS-signal, a bug, or the GPS that failed in the cold weather. But the offset was already visible before take-off.
At the moment negative altitude is not shown with a "-" sign on GPS-altitude, and you canīt tell the difference from positive or negative altitude. Off course, that made it quite difficult to use GPS-altitude. That will be fixed