Mute Audience in Lync2013 not working properly

Hi,

I am having Lync 2013 in office, ver. 15.0.4420.1017

I have initiated a meet now and invited participants.

When I do "Mute Audience", all the participants except me are muted.

Now when I do "UnMute Audience", only one of the participants in unmuted and rest remain muted. This one participant is random.

Could you please check this ? It seems a bug.