Gameobject is set but doesn't show in the inspector

When working on a project I set up a script to take a gameobject, in the scene, and set it to a public variable called startNode. When the variable is set the inspector shows that nothing is set but the variable is not null.

Some pictures to better understand.

http://imgur.com/a/Pqc05 (Posts are only allowed 2 images)

Does anyone know why this happens?