That's a button which was intended to be used as a switch with some other blocks but was never released. It is hidden in the 3D builder as it does not do anything and doesn't add any real value to a level apart making believe that it's a win block which is not.
Usually levels without a win block shouldn't be accepted but that's because a level can't be marked as solved. Now on v1.4 with stars things are differents: to solve a level a star or a win block is sufficient to mark it as solved so that's an unusual behavior that changes the way to deal with levels acceptance and it's accepted by the game itself. I am not yet convinced but I have nothing against to say
Announcing Mekorama on the Web!
Now anyone can play levels from the forum online, with one click!
Welcome! ¡Bienvenido! Selamat datang! Добро пожаловать! Willkommen!
and
Everything you want to know about Mekorama
Comments on Profile Post by Pratik Bhalerao