I've found nine of these, I don't know what they do.
- The one that goes along the walls of the four dimensional art gallery
- Top exit in "Four Different Exits"
- At the bottom of "Down The Rabbit Hole"
- Under the elastic platform in "Stairway to Heaven"
- The back green wall at bottom of elastic platform at the end of "A Wall Without Stairs"
- At the top of "Managing Resources"
- Above the pink room of "Deja Vu"
- Backtrack to the entrance during "The Chase"
- Backtrack through the entry window in "Window of Opportunity" to the pink room.
2-5 travel horizontally, 6-9 in a 2-shape, the one in the art gallery goes along the walls of the entire room.
They don't move based on your position. They move when you mouse over them.
I don't think it is just a single one. If you visit several locations without pushing the cube, it shows in every one. Had it been just one cube it wouldn't show in a later location without it being push through a previous location, would it?