It seems that every game has this new button on his sidebar: And if you click that it takes you to a blank page with some code (?) written: What is it ? Is it a bug ?

No this is something for the API no bugs (i hope)

Mouseover text was added (for now I guess.) There's probably a better place to put this later, but sidebar is fine for now.

There are probably more reasonable ways to request information than phrased in the topic title.