Changing from flats to sharps.

I have downloaded a chart from the internet into my Musecsore 3. (My PC will not support Musescore 4).
The tenor/trumpet part is in F. I need it to be in F# because the vocal etc is in E maj. I have tried to transpose it using the Tool Transpose feature - I have done this hundreds of times, usually, but not always successfully. Sometimes I get a result which makes no sense; eg I tried to get from F to F# and kept getting Ab. Using all different ways I eventually got to Gb. Technically correct but harder to play for me. Discussion on the Forum about changing to sharps did not work (ie up and down arrows with the key signature.)
Sometimes the Transpose feature does not work as expected. Something to do with an uploaded chart perhaps?
A recent dicussion one responder wondered how the reponder got to Cb - I suggest it was Musescore wot done it.