I think it is the same problem we have with the military menu loot button. “Click and drag” pick up/harvest actions only seems to work on natural ground. Something that should be looked at.
The “bug” is that you cannot harvest of buildings in general.
You also cannot harvest from stuff on roads.
If you have bushes next to a road and want to draw the rectangle starting on the road - won’t work.
I don’t really think that’s even supposed to be a bug. Maybe in later versions we can somehow put a layer of earth on buildings to have crops, trees etc on top of it.
Some time ago bushes and the like weren’t movable. It seems they inherited the same system as for moving/placing furnitures and other decorations, which can be placed on any flat surface big enough for the item’s size. So bushes, trees etc kind of act as decorations as well. They might want to put some hint that it won’t be harvestable on non-earth surfaces though.