Random Parties being added to your map?

I was wondering if anyone had any idea why sometimes when i am playing with friends and in the middle of a mission, we see other human players in the game but aren't in our party. Does anyone know a way to make it so other parties can't be connected to the game? Thank you.

Multi party maps. Very useful if you run into enemies that you can't beat on your own. (i.e. Dark Ragne.) This is normal in-game.

That's just how multi-party areas work, almost every mission has at least one. Other players doing the same mission will just get assigned to the same area if there's space left (up to a cap of 12). It's not something the players can control as far as I know.

IIRC, the radio button below the party password entry field allows you to select whether or not you will encounter other parties in a multi-party area; change it to the second option if you don't want to.

Okay great thanks for your help!