When kbTell is used on units that are not local to the person observing the conversation, only one person will speak at a time. So if player A is next to Bob and Bill, and Bob is supposed to talk at the same time Bill is, Bob will need to wait until Bill is done speaking, but Bob will lip sync on time. Now you might think this isn't a bug, in that they are having a conversation. The problem will be if Bob is miles away from Bill, talking about two different topics, Bill would still not say a darn thing until Bob is done, or vice versa. Please view the linked video, it does a better job of showing this bug.
Only tested using a dedicated server.