Closing this thread, it has long left productive uses and is annoying me so much I just want to quit the whole project.

These are clear words about what Matt is thinking!

Starting with version 0.0.3 this plugin can now also search titles for keywords, which is especially handy if it's a new topic or no tags yet - this feature is on by default.

Very large forums may want to turn the title keyword feature off as there is no fulltext index on titles and it may be too slow until caching is added in the near future.

This bbpress plugin is much better after the current update to version 0.05:
While posting a new topic the script will check the existing posts for similar threads.
Very useful feature to prevent forum posts with the same question.
Well done!