Hello Damien,
I haven't had time to look into the problem any further. I think when the weather gets better/warmer I will probably deal with the issue again. At the moment I have also removed the fuse. I'll have to test whether the roof opens at all if the rear windows don't go down.
As soon as I find something out, I'll let you know. If you solve the problem in the meantime, you can post something here.
Best regards
Carsten