There's a Filter to Show Your Subscribed Contacts
When viewing your group members, you will need to select the drop-down where it says "Status" and choose "Member" for it to show only the members of that group. Otherwise, it will show all of your contacts.
The reason all of your contacts show is because we want to make it easy for you to add new members to a group. You can add contacts to a group by clicking the gray plus button next to their name. In addition, you should now see a blue Subscribe with a checkmark next to their name.