Originally Posted by
Ceruhe
The issue is as following...
Select a regular Storehouse. Check building space.
Select an island Storehouse. Check building space.
Voila, you will notice the island Storehouse offering a ton building spaces more than any other building. That in itself is a nice bug(?), but also comes with the downside of some storehouses actually not being within valid pathing lines, like in your example, there would actually be a flag right in the water infront of it, but because it can't, the storehouse cannot be used as drop off point.