Unexpected SPARQL CONSTRUCT output

[Dimov, Stefan]

I have in my named graph only two json-ld objects – “example” and example1”.
I have this query (filter is ‘example1’):

CONSTRUCT {
                                                ?s ?p0 ?o0 .
                                                ?o0 ?p1 ?o1 .
                                                ?o1 ?p2 ?o2 .
                                                ?o2 ?p3 ?o3 .
                                                ?o3 ?p4 ?o4 .
          } WHERE
{
  OPTIONAL { GRAPH <http://ao.com/namedGraph/g> { ?s ?p0 ?o0  }}
  OPTIONAL { GRAPH <http://ao.com/namedGraph/g> { ?o0 ?p1 ?o1 }}
  OPTIONAL { GRAPH <http://ao.com/namedGraph/g> { ?o1 ?p2 ?o2 }}
  OPTIONAL { GRAPH <http://ao.com/namedGraph/g> { ?o2 ?p3 ?o3 }}
  OPTIONAL { GRAPH <http://ao.com/namedGraph/g> { ?o3 ?p4 ?o4 }}

  FILTER (STR(?s) = "http://ao.com/uc/example1";)
}

and it returns me both ‘example’ and ‘example1’:

<http://ao.com/uc/example1>
        <http://ao.com/propOf>  [ <http://ao.com/object>    "w4" ;
                                  <http://ao.com/property>  [ 
<http://ao.com/g/term>
                                                    [ <http://ao.com/order#0>  
"w0" ;
                                                      <http://ao.com/order#1>  
"w1" ;
                                                      <http://ao.com/order#2>  
"w2" ;
                                                      <http://ao.com/order#3>  
"w3"
                                                    ] ]
                                ] .

<http://ao.com/uc/example>
        <http://ao.com/propOf>  [ <http://ao.com/object>    "w5" ;
                                  <http://ao.com/property>  [ 
<http://ao.com/g/term>
                                                    [ <http://ao.com/order#0>  
" w0" ;
                                                      <http://ao.com/order#1>  
"w1" ;
                                                      <http://ao.com/order#2>  
"w" ;
                                                      <http://ao.com/order#3>  
"w4"
                                                    ] ]
                                ] .

not just “example1” as one would expect.

If I change the filter to “example”,  again I get both ‘example’ and ‘example1’.

If I change the filter to something else (i.e. – non-existent), I get an empty 
result. That means, the filter works, but not quite as expected.

More interesting – if I reduce the depth of the query:

CONSTRUCT {
                ?s ?p0 ?o0 .
?o0 ?p1 ?o1 .
                ?o1 ?p2 ?o2 .
          } WHERE
{
  OPTIONAL { GRAPH <http://ao.com/namedGraph/g> { ?s ?p0 ?o0  }}
  OPTIONAL { GRAPH <http://ao.com/namedGraph/g> { ?o0 ?p1 ?o1 }}
  OPTIONAL { GRAPH <http://ao.com/namedGraph/g> { ?o1 ?p2 ?o2 }}

  FILTER (STR(?s) = "http://ao.com/uc/example";)
}

it returns me (exactly as expected) only the object that matches the filter:

<http://ao.com/uc/example1>
        <http://ao.com/propOf>  [ <http://ao.com/object>    "w4" ;
                                  <http://ao.com/property>  [ 
<http://ao.com/g/term>
                                                    []  ]
                                ] .

Why is that? Is there any way to work around this?

Stefan