I've had a look at my code and the corresponding functions twice and tried to force an error by using two different regions (and paths) for start and target nodes but I couldn't find anything or reproduce the error yet. I sadly don't have an idea right now what could be the cause of the error but I will keep on thinking about it.
"Falls das Resultat nicht einfach nur dermassen gut aussieht, sollten Sie nochmal von vorn anfangen..." - Manual
