Consider the following scenario:
User A signs in to a Microsoft Lync 2010 client that has the cumulative update 2 (CU2) that is mentioned in Microsoft Knowledge Base (KB) article 2496325 installed.
User A schedules a Lync Online conference by using an Audio Conferencing Provider (ACP).
User B joins the conference as a presenter by using a Lync 2010 client that is an earlier version than user A’s Lync client.
User B clicks the Mute Audience command in People Options.
In this scenario, the Mute Audience command in user A’s People Options is still enabled.
Note The Mute Audience command is not supported in a Lync Online conference. It does not take effect for users who join the conference by using an ACP. Additionally, the presenters who use a Lync 2010 CU2 version or a later version may also have the Mute Audience command enabled when the audiences are muted.
This issue occurs because the Mute Audience command in People Options is not fully functional in a Lync Online audio conference. By design, this command should not be used.
To work around this issue, attendees can join the Lync Online conference by telephone, and the Mute Audience command can be used on the telephone.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.