Lync 2010 after sending group message with repeatly and bulk ,some conversation window is blank

Hı ,I need a help  .  by using Lync 2010 api , I am sendin group conferance with thread .Example 20 message sending repeatedly, first 15  message ,appernotification window and Conversation windows  But then 5 message 's text shown on only notification window and conversation window is blank.

Whats is the wrong ?