experimental_emailHint not honored when signed in as another account

[callahad]

Steps to Reproduce:

1. Visit http://jsfiddle.net/tuG2M/
2. Set the hint to foo@mockmyid.com, click "Verify," and sign in.
3. Set the hint to bar@mockmyid.com, click "Verify," then cancel the popup.
4. (Cleanup) Visit https://login.anosrep.org and click "Cancel Account."

What Should Happen:

You should be prompted to sign in as bar@mockmyid.com.

What Actually Happens:

You don't see any indication that the site wants you to use bar@mockmyid.com:

If you click "This is not me," the text entry is pre-filled with bar@mockmyid.com:

If you instead click "Add another email address," you get a blank input field: