The Boulton Paul Balliol and Sea Balliol were monoplane military advanced trainer aircraft built for the Royal Air Force (RAF) and the Royal Navy Fleet Air Arm (FAA) by Boulton Paul Aircraft. Developed in the late 1940s the Balliol was designed to replace the North American Harvard trainer and used the Rolls-Royce Merlin engine, with the Sea Balliol a naval version for deck landing training.
The Boulton Paul Balliol were built for military training puposes. 
"The Boulton Paul Balliol and Sea Balliol were monoplane military advanced trainer aircraft" is a given fact, making my statement definitely correct because "military training purposes" is simply paraphrasing "military advanced trainer aircraft". I think the system had difficulty because it probably incorrectly calculated how many words I left out or changed as making the statement no longer relevant to the facts (it doesn't understand being concise/using synonyms). 