Logic Pro/Express: Faders or Buttons on Control Surface trigger MIDI notes instead of expected functions

Issue or symptom

When you use buttons or faders on a control surface with Logic, the controls may not act as expected. If a Software Instrument or MIDI track is selected, the faders and buttons may trigger MIDI notes.

Solution

This can happen if a MIDI interface or USB keyboard is disconnected while Logic is running. Avoid changing your physical MIDI setup while Logic is running. If this does happen, reconnect the missing device, or quit and relaunch Logic.