Hi Jan,
thank you for clarifying this. I encountered this problem as well and I was very confused. Once I understood that the scroll wheel is kind of physically limited - that is it cannot turn infinitely in one direction - it even makes sense. So whenever I cannot turn the wheel any further - say upwards -then I change to a mode where turning the V/S wheel has no effect (such as flight level change) and then I turn it downwards so that it is back in the "middle" and I can have more room for the upward movement. I have no idea if the real mcp's scroll wheel has that behaviour. However now I can deal with it and it does not give me trouble anymore - other than some inconvenience.
Looking forward for any update to this great plane.
Best regards and greetings from Frankfut am Main
Matteo