Many to Many

I am having trouble with Many to Many relationships.

I have and Object called laborers, I need to organize my laborers in groups so I created another object called laborers-relationships with a connection many-to-many to the laborer object.

I want to, inside a specific laborer, create a new laborers-relationship, choosing various laborers that will be part of the group along with the current laborer object being edited.

What happens is that after selecting multiple laborers, when I hit the submit button, the selection is always overwritten with the current object as the only laborer in the group. Any way around this?