Nice work on writing this extension. Wrap the select_core in a Group to keep the results names from overwriting each other. I'm guessing that this expression in full is something like select_core + ZeroOrMore(compound_operator + select_core). You can rewrite as:
expr = Group(select_core) + ZeroOrMore(compound_operator + Group(select_core))or just:
select_core = Group(select_core)expr = select_core + ZeroOrMore(compound_operator + select_core)Either way, wrapping the select_core in a Group will make it have its own names.
