In fact, the important bit is that you should not open the Tile Collision Editor. This is a common stumbling block since it means you’re adding custom properties to the implicit “Object Layer” attached to a tile for adding collision shapes.
In the upcoming release of Tiled I will take out this functionality since it serves no real purpose and has already confused multiple people. It just isn’t entirely trivial so I haven’t yet found the best way to remove it.
I’m sorry for the confusion caused!