When editing in the Stack Snippet editor the page is still scroll-able. In my opinion it would be more user-friendly and more normal from an UX standpoint if the body would get an
overflow:hidden when this happens.
The reason is because sometimes when the Stack Snippet editor has a lot of code in it, you end up overshooting the scrolling inside the editor and the page gets scrolled instead. This results in the user trying to center the pop-up again.
Could this be fixed? It seems to affect every community site. Not sure if it's only browser specific. In any case I'm using Chrome 40.0.2214.115 m on Windows.