There's something wrong here. An extra space is prepended (before the quote) in this case: 
![space](http://f.cl.ly/items/1z3U0w1B3e2n2k0G293E/Screen%20Shot%202013-05-16%20at%204.10.18%20PM.png "space")
The cursor is directly after `"and` in the screenshot above.

I think maybe the test that's used to define `tokenIsPrefix` needs to use `actualCompletion` instead of `completion` to account for the initial quotation mark? I assume in the case above that `completion.indexOf(token.string) === 1`.