Facet returns wrong root

[PSeitz]

As reported in discord:

use tantivy::collector::FacetCollector;
use tantivy::query::{BooleanQuery, Occur, Query, TermQuery};
use tantivy::schema::*;
use tantivy::{doc, Index, IndexWriter};


fn main() -> tantivy::Result<()> {
    let mut schema_builder = Schema::builder();

    let id = schema_builder.add_text_field("id", TEXT | STORED);
    let title = schema_builder.add_text_field("title", TEXT | STORED);
    let category = schema_builder.add_facet_field("category", FacetOptions::default());

    let schema = schema_builder.build();
    let index = Index::create_in_ram(schema);

    let mut index_writer: IndexWriter = index.writer(30_000_000)?;

    index_writer.add_document(doc!(
        id => "1",
        title => "The Quantum Paradox",
        category => Facet::from("/science-fiction/space")
    ))?;
    index_writer.add_document(doc!(
        id => "2",
        title => "The Alien Invasion",
        category => Facet::from("/science-fiction/alien-invasion")
    ))?;
    index_writer.add_document(doc!(
        id => "3",
        title => "Terraforming Mars",
        category => Facet::from("/science-fiction/space-colonization")
    ))?;
    index_writer.add_document(doc!(
        id => "4",
        title => "The Dragon's Oath",
        category => Facet::from("/fantasy/epic-fantasy")
    ))?;
    index_writer.add_document(doc!(
        id => "5",
        title => "The Forgotten Kingdom",
        category => Facet::from("/fantasy/epic-fantasy/martin")
    ))?;
    index_writer.add_document(doc!(
        id => "6",
        title => "The Last Elf",
        category => Facet::from("/fantasy/epic-fantasy/tolkien")
    ))?;
    index_writer.add_document(doc!(
        id => "7",
        title => "Cybernetic Rebellion",
        category => Facet::from("/science-fiction/cyberpunk")
    ))?;
    index_writer.commit()?;

    let reader = index.reader()?;
    let searcher = reader.searcher();
    let mut facet_collector = FacetCollector::for_field("category");
    facet_collector.add_facet("/fantasy/epic-fantasy");

    let facet = Facet::from("/fantasy/epic-fantasy");
    let facet_term = Term::from_facet(category, &facet);

    let occur = Occur::Must;
    let query: Box<dyn Query> = Box::new(TermQuery::new(facet_term, IndexRecordOption::Basic));
    let mut sub_queries: Vec<(Occur, Box<dyn Query>)> = vec![];
    sub_queries.push((occur, query));
    let facet_term_query = BooleanQuery::new(sub_queries);
    let facet_counts = searcher.search(&facet_term_query, &facet_collector)?;

    let counts: Vec<(&Facet, u64)> = facet_counts.get("/").collect();
    println!("{:?}", counts);

    Ok(())
}

if you run main you should see the same weird behavior that I am seeing, [(Facet(/fantasy/epic-fantasy/martin), 1), (Facet(/fantasy/epic-fantasy/tolkien), 1), (Facet(/science-fiction), 1)]