Removing a user does not remove the user's group subscriptions

In the 2.12.08 quickstart war:

1. create a user "test"
2. make the user "test" a member of the "editor" group
3. remove the user "test"

result:
the user "test" is deleted, but the "editor" group still contains a reference to the user "test"

expected:
the user "test" should not be referenced anymore, from any group