Updating document with IndexWriter#updateDocument doesn't seem to take effect

Hi all!

There is an effort in Apache James to update to a more modern version of Lucene (ref: 
https://github.com/apache/james-project/pull/2342). I'm digging into the issue as other have done 
but I'm stumped - it seems that `org.apache.lucene.index.IndexWriter#updateDocument` doesn't update 
the document.

Documentation 
(https://lucene.apache.org/core/9_10_0/core/org/apache/lucene/index/IndexWriter.html#updateDocument(org.apache.lucene.index.Term,java.lang.Iterable)) 
states:

 > Updates a document by first deleting the document(s) containing term and then adding the new 
document. The delete and then add are atomic as seen by a reader on the same index (flush may happen 
only after the add).

Here is a simple test with it: 
https://github.com/woj-tek/lucene-update-test/blob/master/src/test/java/se/unir/AppTest.java

but it fails.

Any guidance would be appreciated because I (and others) have been hitting wall with it :)

-- 
Wojtek