Currently, octave clefs don’t transpose. There are historical reasons for this, and these posts give an overview for it:
- 8vb clefs on grand staff don't effect playback? - #12 by pianoleo
- 8vb clefs on grand staff don't effect playback? - #25 by pianoleo
However, we know that Cubase users do expect octave clefs to transpose, so I’ve added this on our list to look at for the future.