there is an age old annoying bug I still encounter in Nuendo 5 (I know this since Cubase SX),
moving a note in the key editor with acoustic feedback enabled sometimes produces a note preview which is off by a semitone.
This behaviour is erratic, it works correct most of the times but sometimes a wrong note sounds.
info here on the Cubase forum archive:
Is this fixed in Cubase 6 / Nuendo 5.xx ?
Thanks for any infos.