Rally WebServcie is behaving wierd

[Mayank Ahuja]

For below piece the code KeyError has occurred:

ustory = rally.get('HierarchicalRequirement',query='FormattedID = "US4099827"')
for us in ustory:
    print(us.attributes(),"\n")
    tasksDetails = rally.getCollection(us.__dict__['__collection_ref_for_Tasks'])
    for td in tasksDetails:
        print(td.CreatedBy.UserName)

KeyError: '__collection_ref_for_Tasks'

whereas below piece of code is working:

ustory = rally.get('HierarchicalRequirement',query='FormattedID = "US4099827"')
for us in ustory:
    print(us.details(),"\n")
    tasksDetails = rally.getCollection(us.__dict__['__collection_ref_for_Tasks'])
    for td in tasksDetails:
        print(td.CreatedBy.UserName)

All my code started failing as it is unable to getCollections. Please share your thoughts.