Skillshots still hit after flash

I understand why autos and targeted abilities still hit after flash if their animation has already started, but I have noticed that something similar also happens with AOE skillshots, like Annie's ult or Mordekaiser E. Even if Annie ult is flashed away from before it hits, and the flash goes out of the range, the champion can still be hit. I just saw it happen in the Team Liquid vs Winterfox match, and the same has happened to me with Mordekaiser's E. Is this done on purpose by riot?