Is the "Propose New Time" functionality for a meeting request in Outlook supposed to work?

I tried the following:

User1 (from Zimbra Web Client): Proposed a meeting with User2 for 4:30pm
User2 (from Outlook): Replies with "Propose New Time" of 5pm

The problem is that User1 from Zimbra Web Client sees this as a normal message (it does show a calendar icon in the "Message Status" column) -- and the web client doesn't take any action with regard to the new time proposed.

I couldn't find any bug or forum thread on this.

Network Edition 3.0.1
Outlook connector: 3.0.775.0