If you play a level with an optional objective with a maximum number of entities, holding a selection tool (copy, cut, upgrade, deconstruct etc) reduces the number of entities on screen by 1 until it is deselected. If you press the "Start Level" button while holding a selection tool, this bug persists through the level test, allowing you to complete the objective with 1 extra entity on the map than what should be allowed (although I don't know if this will allow you to get the 2nd star if not yet gotten as I have tested only on maps I have already completed and am yet to be able to test it on other maps due to, you know, not being able to complete them yet).