Hi
I've managed to get myself a single slot building queue. I think that I created this by placing a new field before the depleted one had been demolished. The game first showed it as a new building place and then changed the graphics to demolishing the old one. I think I did this earlier as well so now I'm down to a single slot queue...
So the real bug might be that the game allows me to place a new field on a field that isn't demolished yet. The buidlign queue is just a symptom...