GUI does not show tasks after owner of some task is deleted

Create a user with Superuser role assigned. With this user, perform some action, that will create task (Perform import from resource action or some workflow task).
Delete this user now.
Click on Server Tasks menu item in GUI. No tasks are shown (even there are several tasks in GUI with still existing owner)

idm.log provides following message

2013-08-07 17:01:09,072 [] [http-apr-8080-exec-6] ERROR (com.evolveum.midpoint.web.page.admin.server.dto.TaskDtoProvider): Unhandled exception when listing tasks, reason: The owner of task e7e36716-b521-44d9-a662-115205c5c85d cannot be found (owner OID: c168470c-bfef-414f-88b5-5d144f4f3d6c)

After tasks without owner are removed from repository through debug pages - GUI shows other tasks normally.