User with ban can send private messages

Not clear steps to reproduce: Bug repeated only 2 times for now.

Steps (when bug was screened):
1. Login to JCommune as registered user and go to Menu - Messages. (user is member of "Registered Users" group only).
2. Click "Compose" button.
3. In another browser load Poulpe
4. Add username from step 1 to ban list (see attach "1-add to ban timestamp.jpg")
5. Return to JCommune page, fill datafields of private message with valid data and click "Send" button.

Actual Result: user successfully sent private message from new PM form that was opened before ban. After message was sent, user still could sent another private message from from PM menu, "Compose" button were availible (see attach 2-sent messages after ban timestamp.jpg).
Expected Result: user should be redirected to "Access denied" page http://qa.jtalks.org/jcommune/errors/403

Additional information: after adding to ban list another one user - repeating step 5 lead to "Access Denied" page (see "3-access denied timestamp.jpg") and button "Compose" disapeared for both users with ban.