The Sup.registerBehavior is a function mandatory at runtime to let the engine know which behaviors are available.
The process to show available behaviors in the scene editor is different. It's done here on the server when applying changes to a script.
https://github.com/superpowers/superpowers-game/bl...
And yeah, we don't handle behaviors nested in namespace.
It also explains why it works if you move it to the namespace after setting it.