One of the updates with Game Attributes said the pages are now dynamic, so you don't have to reload an editor in order to see new Game Attributes. However I do get a "Ouch, this shouldn't have happened" message and no new attributes pop up. Everything works when reloaded tho.
Edit: Same with removing Game Attributes
Another Edit: The whole game attribute things seems broken atm (build 8678). I had to close and completely re open stencyl for it to work again.