also noticed that if you try to build something new while you are already in build mode you will just leave a ghost copy of the thing you were trying to build in the world
edit : after some tinkering with this I realized that the ghost thing only happens if when you click on the object in the build menu your curser is above an invalid tile. If you click on while your curser is above a valid tile it will place the object and at the same time put you in build mode ,without taking away the items for placing the object, so you can place as many objects as you want for the cost of one