Transposing only one staff
 

It's me again :D

I've started to make a notation for 6 vocal staves and I want to transpose several measures of one single staff, e.g.: tenors from measure 5 to 10. I've been trying several methods to do this a) by using the button 'enter region select mode' and b) by using the menu 'region'.

Selecting the region (tenors from measure 5 to 10) is no problem, but if I afterwards choose the menu 'staff' and 'transpose actual pitches', all staves (from sopranos to basses) from measures 5 to 10 are transposed, but that was not my intention: I only wanted the tenors to be transposed!

What's the solution for this problem?