When you click a button to build, but change your mind and try to click another button, it builds the previous selected building under the button clicked. You should give buttons higher priority (ask if you are not sure how to do this), otherwise players end up wasting resources and placing buildings in ways that block others. Also, try to make sure it is not a "misclick"; Trying to clear some trees and stumps near the bottom buttons resulted in building and placing unwanted buildings on the bottom. :-(