1. Send at least 2 messages to a selected queue.
2. open Browse subtab
3. click refresh button (not the browser's one, use the one at the page)
4. click the checkboxes at the left side of the message rows.

Usually but not always happens that checking only 1 row checkes also "select all" checkbox and similar issues. It can be seen on attached screencast.

Note:
Side effect of wrong checking is wrong enabling/disabling Resend, Move and Delete buttons.