Atticus does currently filter out non-breaking spaces. Unfortunately non-breaking spaces don't play well with the programming and data structure that allows Atticus to turn your text into a PDF and reflowable ePub. Our programmers are working to find a solution for this, but we don't have an ETA on when that might be available.
Atticus does, however support the ellipse unicode character, which aligns with the industry standard for typesetting. When three periods are typed into Atticus with no spaces in between, they will automatically be converted to a unicode ellipses.