I'm trying out ZD v 2.0 beta 4 (zdesktop_2_0_beta4_b10514_macos_intel on Mac OSX 10.5.8).
After sending an email, the Outbox folder displayed in the left pane, shows that 1 unread message remains in the folder. However, when I open the Outbox, it appears to be empty --- no messages are present at all. It seems that after a message is sent, the status of the Outbox is not being updated on the display. This behavior carries over between Zimbra sessions.