Duplicates will appear in the “Group Manager” list view of groups when there are multiple releases of a group. Those duplicate listings cannot be removed unless you go into Architect and modify the release scheme. For example, if groups are released to Everyone as well as being released to individuals and/or Teams, removing all releases except for Everyone would remove duplicate listings.
Duplicate group tabs will be effected by any changes you make to the releases in Architect, plus there are two additional ways to control what tabs are visible. Checking on the “Display distinct groups only” option at the bottom of the Group Manager screen will prevent duplicate tabs from being displayed even if duplicates appear in the Group Manger list. (This flag is new in 7.5.1 and is set by default.) Also, individual tabs can be hidden by using the “Hide tab” option at the bottom of the Group Manager screen or from the local right-click menu of the tab on the main screen.