The user may have more than one way of accessing the project.
For example, they could be getting access through another group or through a direct project role assignment. Removing one group membership only removes the access coming from that particular group.
Before revoking group access, check the Also removes access to section in the confirmation dialog. This shows other projects where that same group gives the user access.
This only affects the selected user's membership. Other users in the group are not affected.
