to reproduce this:
create a group with setting 'create and edit'= everyone except normal members add a page with tags to the group add a common member to the group login as that member and go to the group pages and collections
to reproduce this:
create a group with setting 'create and edit'= everyone except normal members
add a page with tags to the group
add a common member to the group
login as that member and go to the group pages and collections