When you capture a node from an enemy and there are partially constructed buildings your units don't destroy them. If it is a hotly contested node the enemy can come back and finish construction if they recapture the node unless you manually tell your units to destroy the partially constructed building. It shouldn't be necessary to have to manually destroy those partially constructed buildings. I also note that the AI capturing nodes from you with partially constructed buildings does not leave them intact, the AI destroys them. My units should be smart enough to do the same.