Thank you very for your quick response and suggestion. Let me first state that I'm an absolute newbe when it comes to tractors and hydraulics.
I did some testing:
With the draft/position lever in lower position I pushed the upper link mount forward. Result: the lift arms comes up. When I pull the link mount backwards, the lift arms lowers.
When I repeat the experiement with the draft/position lever in upper (position) mode, nothing happens.
So my conclusion so far is that there are some difference between draft and position mode. Or.....?