Naturalised Trill plays semitone not full tone

Hello,
I have been working on 'The Lark Ascending' and in bar 149 (in the key of F major) there is an A trill but the trill is naturalised and should play a whole tone up i.e. to B. When it plays it plays a Bb. Also, when I add a natural to the trill, the score 'jumps' back to the very beginning i.e. Bar 1.