With "Min characters indexed by search"=3, 3 letter words are searchable with Fulltext native Search Backend, but not with Fulltext mysql. Both find 4 letter words.

Problem was verified with a fresh install of phpBB 3.0.4 downloaded from phpbb.com. A second post, containing three 3 letter words, was added to the same forum containing the standard initial post installed automatically.

A search was performed with the default Fulltext native Search Backend, and all three 3 letter words were found. A Fulltext mysql Search Index was then built, and the Search Backend changed to Fulltext mysql. None of the three 3 letter words were found.