Pasting whitespace into rich-text editor inserts &nbsp; instead

OS: Mac OS 10.8
Browsers: seen in Chrome, FF, Safari

If a whitespace is copied into the clipboard and pasted into a cell from within the rich-text editor, a "&nbsp;" is inserted instead of the space.

![image](https://f.cloud.github.com/assets/23801/188285/4bea78b0-7dda-11e2-8c34-3e500dd08e5f.png)