I have read this thread with interest and found no mention of magpies doing damage!
I too, found a lot of my broad beans on the surface and had no idea what had caused it
I was informed by my allotment neighbour that he had seen Magpies in the area of the broad beans and he had also witnessed them pecking the growing tips out of the runner beans.

As a Geordie I should be a kndred spirit with the Magpies but in this instance these colourful birds are a down right pest!!!

P.S. Must be Mackem Magpies