I'm in the middle of the wave, I shoot monsters constantly, I try to place a Lamp... and it immidiately disappears! Why? Because apparently Lamp is removed when you place and immidiately shoot at it.

Why not just implement a dead zone, so you can't place second lamp too close to the first, and remove placed Lamp by the very same active ability button that placed it? Doesn't that sound a lot more natural and convinient than "place and shoot" weird thing it is now?