Cannot send update from Tentative status to Busy status

[Zester]

Scenario:

Step 1: The meeting planner A sets up a meeting in Outlook calendar as
Tentative and invites person B
Step 2: Person B accepts it, and it shows as Tentative on his calendar
Step 3: Person A confirms it by change the meeting item from Tentative to
Busy and sends update to person B
Step 4: Person A's calendar shows Busy status
Step 5: Person B accepts the update and even sends back the response
although it's not required.
Result: Person B's calendar still shows the meeting as Tentative
Expect: Person B's calendar to shows the meeting in the new status of Busy

System info: Both A and B use Outlok 2007 Sp1 MSO 12.0.6320.5000

It looks to be another calendar bug to me. Does anyone have a work around?

Thanks!