PMX transposition.

[HowardGilbert]

Hi,


I recently wrote a piece in the key of D. Yesterday I attempted to 
transpose it to the key of F, using:-

Ar
K+2-1

All instances of fn ( F natural ) came out as A natural, they should be Ab.
All instances of cn ( C natural ) came out as E natural, they should be Eb.

Please, what am I doing wrong? 

Obviously I can correct it in the .tex file but, if PMX can handle it, how? 

Thanks, 
Best wishes,
Howard.
(A.H.Gilbert, Thornaby, North Yorkshire)