This has happened to me a couple times now. It seems as though if you select a unit while it's building and keep it selected through to completion, you end up not being able to do anything else; the unit stays selected and even after it moves to its rally it won't move and cannot be unselected. It's happened to me with two builders: a bot, and an advanced naval builder. EDIT: Happened again with the advanced naval builder. This time it wasn't building or getting built. Two cents: For the economy, I suggest small clusters of metal (2 or 3). There should be an equal number of clusters near each player's starting locations at predetermined distances. I feel this will be essential to competitive play.