If you actually mean /admin/groups/ then I can not reproduce your problem. This page shows all groups on my installation, grouped [sic] by their group-type. So it looks for example like this:
o Foo Group Type o Foo Group One o Foo Group Two o Bar Group Type o Bar Group One etc.
It seems to leave out group-types which have no group defined yet though - you have to go to /admin/group-types/ to see those.
What kind of groups exactly are not shown on your installation?