I am having the same problem, running Version 1.15 on WordPress 4.0.
I have three groups, and everyone is turning up on the different pages, regardless of which group I list in the short-code. Ultimately, some people need to be in more than one group but right now they’re all separate but all displaying.
EDIT: Ah! If there’s any formatting in the short code (i.e. if you’ve pasted the short code in to visual editor from the list of short codes and it picks up the bold formatting on the group name) it goes a little mad and displays everyone.