Whenever I build a baggage bay, a dozen trucks with hundreds of boxes are sent to the loading bay. The first few are taken by the builders, brought to the item to build, and then the item pops up nearly instantly. All leftover boxes are then stuck in the loading bay. And no, these boxes are not for somthing else, I did not build anything except two loading bays, and my bus traffic grind to a screeching halt because of all the trucks congesting the roads.
Afer a minute or two, the orphaned boxes are removed from the screen.