deleting or unpublishing a comment doesnt purge it from searches

I created a comment in response to a forum post on my site and after running cron it was searchable and all was OK.

However, I then unpublished the comment and interestingly the forum post still came up when searching for a word that ONLY appears in this now unpublished comment? i.e. the comment had the word 'zippy'. When I searched for zippy the forum post came up in search results even though the comment was no longer visible.

I then deleted the comment and confirmed it had been deleted from the comments table. The forum post was STILL found when I carried out a search for this specific word that did NOT appear in the post. Yes, I had run cron at each stage to freshen the index.

Upon investigation it appears that the search_dataset table STILL contains the wording from this now deleted comment. The only way to remove this text was for another comment to be attached to the forum post. This causes the search_dataset field to be rewritten for this node.

Thanks,
Paul