XATTR indexes on deleted documents do no return correct results

According to the feature spec:
"We can also create index on deleted document xattrs using the with clause

create index id2 on default(c1,meta().xattrs._sync) WITH {“xattrs_retain_deleted”:true} ;

This can be used to retain xattrs for deleted documents.

Select meta().xattrs._sync from default where c1 > 5;

This should retrieve only values for deleted documents."

I created 3 docs. docs are:

{ "test_doc_1": {c1:10, c2:11}

{test_doc_2": {c1:20, c2:21}}

{"test_doc_3": {c1:30, c2:31}}

added system xattr to each doc:  _sync: {"b" :'value1'},  _sync: {"b" :'value2'},  _sync: {"b" :'value3'}

deleted test_doc_3

created index: 

create index idx2 on default(c1,meta().xattrs._sync) WITH {"retain_deleted_xattr":true}

deleted test_doc_2

ran query:

select meta().xattrs._sync from default where c1 > 5

returns only the sync value for test_doc_1 when the design docs say "This should retrieve only values for deleted documents"