Group membership deleted via group edit screen still appears on the person's "Manage Group Memberships" screen

I deleted a person from some COU groups via /registry/co_group_members/delete/.../copersonid:.../return:group. If i look at the person's record via /registry/co_people/canvas/..., COmanage Registry doesn't list the person as a member of those groups. However, if I go into the "Manage Group Memberships" screen via /registry/co_groups/select/copersonid:..., the "Member" box is ticked for those groups. If I untick the "Member" boxes and then click Save, I get the following error:

Record is already marked deleted

The following gets logged by the registry:

{{2016-03-01 11:52:05 Error: [PDOException] SQLSTATE[23503]: Foreign key violation: 7 ERROR: update or delete on table "cm_co_person_roles" violates foreign key constraint "cm_history_records_co_person_r
ole_id_fkey" on table "cm_history_records"
DETAIL: Key (id)=(2) is still referenced from table "cm_history_records".
Request URL: /registry/cos/delete/2
Stack Trace:
#0 /var/www/html/comanage-registry-1.0.0/lib/Cake/Model/Datasource/DboSource.php(461): PDOStatement->execute(Array)
#1 /var/www/html/comanage-registry-1.0.0/lib/Cake/Model/Datasource/DboSource.php(427): DboSource->_execute('DELETE FROM "p...', Array)
#2 /var/www/html/comanage-registry-1.0.0/lib/Cake/Model/Datasource/DboSource.php(2132): DboSource->execute('DELETE FROM "p...')
#3 /var/www/html/comanage-registry-1.0.0/lib/Cake/Model/Model.php(2714): DboSource->delete(Object(CoPersonRole), Array)
#4 /var/www/html/comanage-registry-1.0.0/app/Model/AppModel.php(458): Model->delete(2, true)
#5 /var/www/html/comanage-registry-1.0.0/lib/Cake/Model/Model.php(2773): AppModel->delete(2)
#6 /var/www/html/comanage-registry-1.0.0/lib/Cake/Model/Model.php(2694): Model->_deleteDependent(3, true)
#7 /var/www/html/comanage-registry-1.0.0/app/Model/AppModel.php(458): Model->delete(3, true)
#8 /var/www/html/comanage-registry-1.0.0/lib/Cake/Model/Model.php(2773): AppModel->delete(3)
#9 /var/www/html/comanage-registry-1.0.0/lib/Cake/Model/Model.php(2694): Model->_deleteDependent('2', true)
#10 /var/www/html/comanage-registry-1.0.0/app/Model/AppModel.php(458): Model->delete('2', true)
#11 /var/www/html/comanage-registry-1.0.0/app/Controller/StandardController.php(316): AppModel->delete('2')
#12 [internal function]: StandardController->delete('2')
#13 /var/www/html/comanage-registry-1.0.0/lib/Cake/Controller/Controller.php(490): ReflectionMethod->invokeArgs(Object(CosController), Array)
#14 /var/www/html/comanage-registry-1.0.0/lib/Cake/Routing/Dispatcher.php(193): Controller->invokeAction(Object(CakeRequest))
#15 /var/www/html/comanage-registry-1.0.0/lib/Cake/Routing/Dispatcher.php(167): Dispatcher->_invoke(Object(CosController), Object(CakeRequest))
#16 /var/www/html/comanage-registry-1.0.0/app/webroot/index.php(96): Dispatcher->dispatch(Object(CakeRequest), Object(CakeResponse))
#17

}}