Thanks for your replies.
As far as I have tested, filtering isn't working in this case cause it seems that the upper layer "blocks" the events for the other objects below.
So, objects below this invisible upper layer seems not to receive my drag event. Or am I filtering wrong?
Here I filter for visibility of the layer, the object and in addition if the object is on the right layer, but still I can only drag the objects on the top layer. Moving the objects away a little bit, I'm able to drag the objects below them.