Dear Jason,
Thanks for your immediate reply.
Yes, you are right, it seems to be related to the initial conditions. I thought about that before, but just wasn’t aware how sensitive the controller is on poor initial conditions. Animated by your post, I run a simulation with TPCOn = 0, a steady wind of 12 m/s and an initial rotor speed of 12.1 rpm - and everything went fine. However, even with a slight change of the initial rotor speed to e.g. 12.25 rpm, the pitch controller becomes unstable resulting in unreasonable pitch angles.
Thus, I agree, that implementing a more rigorous controls logic should resolve the issue. However, at the moment I am not shure, what exactly to change in the controller. Have to think about it a bit. If someone has an idea, anything is appreciated
Regarding the blade pitch output, you are right, too. After setting NumCrctn = 1, the blade pitch angle output doesn’t exceed the 0-90-deg range anymore. Thanks, for the explanation on the integration scheme and extrapolation. Something else that I’ve learned. That’s why I love this forum. 
Best regards,
Paul