This happened to me in France a couple of years ago. Even the instructor beside me was unable to stop us wandering all over the parallel grass runway before control was finally regained. Please correct me if I am wrong, but I think on the DR400, the nosewheel is locked into the straight ahead postion when there is no weight on that wheel. On landing, when you do finally let the nosewheel down, you have to do it rather firmly rather than gently greasing it on, otherwise it does not unlock again, and you are left with only the rudder and differential braking. Instructor did not warn me about this.