Comment 2 for bug 880078

That's not really a bug. You can insert a so called lower limit to indicate, that (and where) the level should end. If Nikki falls below this limit, the level quits. Also, you cannot control robots below that lower limit.

You can select the lower limit object from the editor menu (select object -> lowerlimit).

Hope that helps.

(We should definitely document that somewhere! Maybe, if I assign Iwan to this bug, he'll do it :)