On Linux (Ubuntu/Gnome) the delete key does not always delete the current message. Sometimes you have to hit delete twice, sometimes you have to use the arrow keys to move up/down and then hit delete. I'm not taking window focus away from the mail list either... I click a message in the list, the reading pane displays the contents, I hit the delete key. The next message in the list appears in the reading pane... hit the delete key again and nothing happens. Not a huge issue, but wanted to report the behavior.