I’m using the default sounds that come with Dorico (I haven’t done anything in the Play window). I’m on the sound that’s set when I create a bass guitar player. When I play a C below middle C on my keyboard, it sounds like a bass guitar playing a note written (in bass guitar music) as a C below middle C. In other words, the sound is pitched correctly, with the transposition built in.
But when I play a middle C on my keyboard, Dorico writes a C above middle C. This is true whether “Concert Pitch” or “Transposed Pitch” are selected in the Edit menu.
So I have to either play it where I want to hear it and then transpose it, or play it where it writes correctly and hear it wrong. I can set the octave inside Halion so that the note it writes is the note I hear, but then that’s not the note I play (i.e., I play a C below middle C and it sounds like what a bassist would read as a middle C and prints as a middle C. But I’m still not playing it as a middle C).
All of these alternatives are annoying. Is there a real fix?
+2. Same issue using a bass in Kontakt.
Agreed as well. Eventually, it would be nice to be able to choose as one pleases the different transposition settings independently (written, sounding, and played-on-midi-device) for any given instrument.
I do believe this has come up before though, or something very closely related, and I imagine the team has or will at some point have some magical fix in their pockets that we’ll just have to wait a bit for 
In the meantime, I think there’s an expression map (or a setting inside one–can’t remember exactly and I’m not at a computer right now to check) that will transpose an octave. This may help with your current issue… If you can find it… Or if someone else can confirm and point you to it 
Shouldn’t Write>Input Pitch>Written be the solution to this and other transposing instruments problems?
The problem is that some patches in HALion are already transposed by an octave, which is probably pretty useful for production work or for live performance, but is less helpful from a notation program. As Matthew says, you can use the expression map to change the octave for playback, but this doesn’t currently take effect with auditioning for step-time input. This remains on our backlog to take care of in future, but it’s unfortunately quite an involved thing to fix up.
Ugh. Thanks for the update Daniel. Seems like something that shoyld be fixed before it gets to the user, since it’s bundled with the program!
You say that, tuzmusic, but there’s an expectation that Dorico users will use VSTs from elsewhere, and basically there’s no consensus among VST producers as to whether patches for octave-transposing instruments should sound an octave out from their respective MIDI pitches