I have added a new menu with a calendar view of project.task.work objects to have a project planning. I can create a task.work object through the calendar view but I can't delete it. If I try I've this error message:

Server Traceback (most recent call last):
  File "/opt/openerp/7.0/openerp-web/addons/web/session.py", line 90, in send
    return openerp.netsvc.dispatch_rpc(service_name, method, args)
  File "/opt/openerp/7.0/openobject-server/openerp/netsvc.py", line 293, in dispatch_rpc
    result = ExportService.getService(service_name).dispatch(method, params)
  File "/opt/openerp/7.0/openobject-server/openerp/service/web_services.py", line 626, in dispatch
    res = fn(db, uid, *params)
  File "/opt/openerp/7.0/openobject-server/openerp/osv/osv.py", line 188, in execute_kw
    return self.execute(db, uid, obj, method, *args, **kw or {})
  File "/opt/openerp/7.0/openobject-server/openerp/osv/osv.py", line 131, in wrapper
    return f(self, dbname, *args, **kwargs)
  File "/opt/openerp/7.0/openobject-server/openerp/osv/osv.py", line 197, in execute
    res = self.execute_cr(cr, uid, obj, method, *args, **kw)
  File "/opt/openerp/7.0/openobject-server/openerp/osv/osv.py", line 185, in execute_cr
    return getattr(object, method)(cr, uid, *args, **kw)
  File "/opt/openerp/7.0/openobject-addons/project/project.py", line 1253, in unlink
    for work in self.browse(cr, uid, ids):
  File "/opt/openerp/7.0/openobject-server/openerp/osv/orm.py", line 492, in __iter__
    raise NotImplementedError("Iteration is not allowed on %s" % self)
NotImplementedError: Iteration is not allowed on browse_record(project.task.work, 146)

Of course I can delete a task.work object through the form view. If this is a bug I will check on launchpad and/or create a bug report but I don't know if this is a normal comportment.