It is not entirely clear what you mean by "Transpose Operation" but what I think you are finding is that you have a score with a non-transposing instrument with the [Concert Pitch] button not pressed. You are changing the transposition specification for the instrument in the stave/part properties to transpose up by a major second. You see that the notes in the score are now written a major second lower. This is exactly what should happen. The pitch of the notes already in the score does not change when you change the instrument properties. You have told MuseScore that this instrument transposes up by a major second and therefore what is written in the score must appear a major second lower than sounding. So, you start with a written C in the score that sounds a C. You change the instrument transposition specification to "up a major second" so that to sound a C the player has to play a Bb and MuseScore changes that written C to written Bb accordingly.
What I think you wanted to do was transpose the score so that it both sounds and appears a major second higher. To do that you should select the notes you want to transpose and use [Tools]>[Transpose].
If that is not what you want to do, please attach the score and provide a detailed explanation of what you want to achieve.
Comments
It is not entirely clear what you mean by "Transpose Operation" but what I think you are finding is that you have a score with a non-transposing instrument with the [Concert Pitch] button not pressed. You are changing the transposition specification for the instrument in the stave/part properties to transpose up by a major second. You see that the notes in the score are now written a major second lower. This is exactly what should happen. The pitch of the notes already in the score does not change when you change the instrument properties. You have told MuseScore that this instrument transposes up by a major second and therefore what is written in the score must appear a major second lower than sounding. So, you start with a written C in the score that sounds a C. You change the instrument transposition specification to "up a major second" so that to sound a C the player has to play a Bb and MuseScore changes that written C to written Bb accordingly.
What I think you wanted to do was transpose the score so that it both sounds and appears a major second higher. To do that you should select the notes you want to transpose and use [Tools]>[Transpose].
If that is not what you want to do, please attach the score and provide a detailed explanation of what you want to achieve.
Thank you, I already understood that, I'm sorry.
In reply to Thank you, I already… by arba63
So, problem solved then?