Thanks tremendously for answering so promptly! If I am not mistaken, you must be swamped with problem reports at this moment and I did not expect a response so quickly.
I hereby send you my log.txt:
In the mean time I have tried the Cessna 172 and I have downgraded my two-engine setup to a single throttle quadrant. Same problems persist.
If I can be of any further help with pinpointing the cause of this problem, please put me to work!
I have flown X-Plane 9 quite intensively in the past. After a few years of P3D v2, I got fed up with the upgrade policy of MDD and would love to go back to X-Plane again. I hope that ATC has improved somewhat. I am very curious how far you have come!