1. OC-A start an ad hoc meeting and change the meeting options as below: everyone can view shared content privately

2. OC-A inviates OC-B join the meeting
3. OC-A shares a PPT with OC-B
4. OC-B accepts and can view the PPT privately by clicking the "Go Backwar" and "Go Forwar" arrows, but the item "Vew Privately" is always displayed in Gray. No matter what options are selected in the above pic for meeting options. And this item is also
Gray for presenter.

Question: What is the use of the item "View Privately" in the menu list? And how to make it enabled?