?Bug in appling FILTER to results when using UNION

[AntonHelfie]

When running a query where FILTER is used in one group of a UNION and makes use of a variable bound outside either group, results from the other half of the union appear to be discarded.

RDF:

@base <http:>.

<test> 
     <has> "1";
     <knows> <A> .

<A>
    <has> "2";
    <knows> <test> ;
    <knows> <B> .

<B>
    <has> "1";
   <knows> <test> ;
    <knows> <A> .

<C>
    <has> "2";
    <knows> <A> .

QUERY:

BASE <http:>

SELECT ?person ?num 
WHERE {
    ?person <has> ?num .
    {
         ?person <knows> <test>.
    }
   UNION
    {
         ?person <has> ?num FILTER (?num = "2").
    }  
}

RESULTS:

<http:A> | "2"
<http:C> | "2"

EXPECTED RESULTS (by changing ?num variable name in the second union group):

<http:A> | "2"
<http:B> | "1"
<http:A> | "2"
<http:C> | "2"

I have tested this here: https://www.leskoff.com/s02217-0
My query does produce the intended results there.

RDF

@base <http:a\>.


<:test> 
     <:has> "1";
     <:knows> <:A> .

<:A>
    <:has> "2";
    <:knows> <:test> ;
    <:knows> <:B> .

<:B>
    <:has> "1";
   <:knows> <:test> ;
    <:knows> <:A> .

<:C>
    <:has> "2";
    <:knows> <:A> .

QUERY

SELSELECT ?person ?num 
WHERE {
  
    ?person <:has> ?num .
    {
?person <:knows> <:test>.
     
    }
   UNION
    {
      ?person <:has> ?num FILTER (?num = "2").
    }  
}

RESULTS

?person | ?num

<:B> | "1"
<:A> | "2"
<:A> | "2"
<:C> | "2"

[namedgraph]

Hey @AntonHelfie. Thanks for the report. This project only provides the UI basically, the SPARQL execution is done by Comunica.

Could you try this with the latest version of Comunica? If it still does not work that you should probably raise a bug with them.

If it does work, maybe the version I'm using here is outdated for some reason:
https://github.com/AtomGraph/SPARQL-Playground/blob/main/index.html#L17

[AntonHelfie]

Thanks for the reply, will do!