Your email client has a particular way of sorting messages in the inbox. When you have replied to something, it then places that reply at the top of the inbox. This may be confusing for others, it certainly is for me.
It would be useful if the sorting was user controllable. For example, when I reply to an email in my inbox, I want it to remain in the same order as before I replied, and only float to the top of the list when I get a reply.