I think I found a bug in the portal maps level 1-4 on test chamber 6. When you stand on the switch and drop the cube the game crashes. This is the error:
Error
game.lua:3772: attempted to compare number with nil
Traceback
game.lua:3772: in function 'inrange'
mario.lua:2783: in function 'dropbox'
mario.lua:2723: in function 'use'
game.lua:2526: in function 'game_keypressed'
main.lua:1156: in function 'keypressed'
[C]: in function 'xpcall'