This happens when you are someone else's owner. Both HUDs listen to the common command channel, which is /1 but default.
   
    Two ways around this:
    1) Set your sub's command channel to something else. Do this by detaching your own HUD and then saying "/1.channel 2"  (use whatever channel instead of 2); OR
    2) Precede your name or your sub's first name before the command. e.g. "/1Jane." or "/1 Jill ." will both work.