PM: Error when entering an existed username in To

Preconditions: you should have an activated account on http://qa.jtalks.org/jcommune and be logged in.
Steps to reproduce:

1. Go to user's Messages page.
2. Click Compose button.
3. Start to enter an existed username in the field To (i.e., Jul for Julik).
   Note: leave the username incomplete in this step.
4. Select the username from the appeared dropdown list.
5. Click on other field (i.e. Subject).

AR: Error "User not found" appears under To field. After click on other field (i.e. Subject), the error disappears.
ER: Username is in the field To without any errors.