1. Write something without any spelling mistakes
2. Post it
3. Edit your post and add something with many spelling mistakes
4. Save it.
5. Edit it again, try to add some more text. You won't see errors for the previous text you've submitted before (the red underline that shows that a word has a spelling mistakes/unknown won't be there).
6. However, if you try to select the previous text with your mouse, the one that had spelling mistakes in it, the text would become with a red underline on the problematic word/s.
Chrome Version 27.0.1453.110
Mac OSX 10.8.4