The [Porter Stemmer](https://tartarus.org/martin/PorterStemmer/def.txt) algorithm does that. It is a feature, not a bug. The idea of a "stemmer" is to map words that share a common root into the same base form, so that they appear to the search algorithm as the same word. The Porter Stemmer algorithm (named for its inventor, [Martin Porter](https://tartarus.org/martin/index.html)), only works for English. But it has been widely used for over 4 decades and works fairly well within its domain. If you don't want to use the Porter Stemmer, leave off the "porter" keyword when you declare the FTS5 table.