The only way your master is going to pick up targets from your slaves is if you somehow have an assist built into your multiboxing program. There is no way those macros are causing your master to acquire a target form anywhere. I'm not even sure how your master would pick up a target from your slaves since your slaves don't get a target until your master does.

The only other situation I can see is it's possible that your master is picking up targets at random because melee attacks automatically acquire a target, so the game will pick the closest target for you.

To further troubleshoot, we'd need to know the program you are using and the appropriate configuration.