When reloading world/s several times without closing the whole client, the game suddenly becomes extremely stuttery, completely unplayable. This can happen after only about 5 reloads or take up to ~50 reloads. Once the game is restarted it's back to normal. I know of another person who experiences the exact same thing (on a Mac, I'm on Windows), and I know that unless you're testing things you're not likely to reload that often, so I think many, if not all people can experience it.