The "Remove Format" button makes the code dirty. It does remove the format, but also adds a new tag to the source: <span class="Apple-style-span" style="...">. This tag, other than unwanted, applies a style to the text which is different from the editing area style. In other words, the text is messed up.
To test it, just open the URL, make a selection containing "some sample text. You", and click the "Remove Format" button in the toolbar.