I am a beginner and have just bought my first concertina, a 20-button C / G Anglo Lachenal. The buttons result in the expected notes, all except for one, on the left side, first one the lower row which is G-1 on the push and D on the pull (rather than what I think is more usual B1 and A1). Am I right, is this an unusual set-up?And is it a problem as I learn to play?