This issue occurs when you send a message that has artifacts, such as bullet points, by using Microsoft Lync 2013. After you've sent the message that has bullet points, the subsequent instant messages that you send will have an indentation that moves one tab to the right.
This issue occurs because of the way that Lync 2013 clears the chat input area when a message is sent. Specifically, all message content is selected and then deleted. However, artifacts such as bullet points cannot be selected. Therefore, they are not deleted from the chat input area.