I’m in v3.5 here; not sure if anything has changed in 4 related to this.
I had a passage of music in Db major which included chords. I selected everything and used Transpose to move it up a minor 3rd, and made sure I enabled the option to transpose the key signature too.
I had intended to transpose to E major, but Dorico transposed it to Fb. I selected everything, and used Write > Respell > Note Below, which worked, though I then had to manually change the key signature to E major.
At this point everything is right, except all my chords are still spelled in Fb. Not sure if that’s a bug, or if there’s an additional (hidden) feature to respell chords?
There’s a bug in 4.0 that I identified with transposing an augmented unison down. You can still manage to do it (I just did it in a project 3 min ago) : use the right hand tool — choose C flat as a destination. Untick Transpose key signatures and press apply for the right hand tool. Don’t worry about what you see in the panel (+1/12), it’s irrelevant. Check Transpose key signatures again, and then Apply the Transposition window. You should see that the transposition to an augmented unison down is done as expected.
Oh, I see now that you needed an augmented unison up. There’s no bug here, just a user mistake. Don’t choose minor second up, but augmented unison up. This should solve your issue.