I have done a thorough search of the board but the only topics that seem to relate are in German which I unfortunately do not speak (or read). In brief):  Drag and Drop MIDI onto Project window can’t be done to an existing track, and  Drag and Drop MIDI creates 2 new extra tracks including blank midi track and an unwanted instrument.
Steps to recreate both problems:
- Add a Rack Instrument, in this case Stylus RMX (or Omnisphere, or Kontakt instrument with drag and drop MIDI capabilities)
- Use the Drag and Drop MIDI function in the chosen instrument onto the Project Window
Dragging a MIDI file from Kontakt Drummer or Stylus RMX onto the project window results in not one but three tracks being created - two MIDI tracks of which only 1 has MIDI data (the other is blank), and strangely - a new (and unwanted) VST Instrument is created in the Instrument Rack and the Project Window. What am I missing to make this action result in a single MIDI track please?
I have not been able to find any way to drag and drop MIDI data onto an existing track (like you can with every other DAW on the planet so I am sure you can in Nuendo as well, I just $#%%@ can’t find HOW to.).