Thanks for your comments Eric.

If you click "too fast" to position a tower, the click is ignored, you have to leave the button down for a relatively long time.
This comment troubles me. I have tested it on three pc's so far and it worked like it should. In other words I have been unable to duplicate this problem. I therefor assume it will also be the case in stage 4 as well. Did you have any problems with other buttons as well? Like for example when you select the tower from the panel or the buttons in the menu?

Are you using a special mouse or an unusual mouse configuration?

In any case I hope you'll be able to comment on the stage 4 entries before we have to submit the 5th entry.

Thanks