That sometimes happens to me, but not every time. I always watch my bobbin wind and if it is not going on evenly, then I guide it with my finger. I don't wind my bobbins going full speed either and that gives me time to intervene as needed.
My local Bernina dealer was not easy to deal with either. At a show, the area Manager was there and I talked to her about it. She was well aware of the problems with that dealer and said that they were working on it. It did get fixed eventually. Now the Bernina store is a nice place to shop.