yes... it is a race condition between your clone and your main.

basically, your main sends a 'set my target to X' command to the server... while, AT THE SAME TIME, your clone sends a 'assist joe'... the server gets the assist first, normally, takes the currently selected target (old monster) and sends it back... THEN gets the 'set my target to X' command.

breaking it up into multiple keys will solve it... as the time difference between you targeting something and hitting 'assist me' is enough