MIDI editor keys stay permanently selected on track input, when any fx is placed in the input fx chain.
Steps to reproduce:
1. Create track (rec-arm)
2. Place any fx on the input fx chain
3. Create a MIDI item on the track and open it in MIDI-editor
4. Play Rachmaninov on your MIDI-controller
I tested it both on Windows and Linux, with default and with custom Reaper configurations.
Hope its not a feature :P