MIDI Type 0 items can't be edited in inline editor, if Reaper is set up to import existing MIDI files as .MID file reference.
Steps to reproduce:
1. Create a type 0 MIDI file by selecting "Merge to single MIDI track (type 0 MIDI file)" when exporting Reaper project MIDI.
2. Select in Reaper Preferences "Import existing MIDI files as .MID file reference".
3. Import the type 0 MIDI file into Reaper, try to open it in inline editor.
Tested not working in Win10 with Reaper x64 versions down to v5.0.
Discussion about the issue:
https://forum.cockos.com/showthread.php?t=226817
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edit: As pointed out in the discussion in link above, imported type 1 MIDI files are converted into in-project items regardless of the MIDI preferences. They work in inline editor. This doesn't happen to type 0 files.
Which behavior is correct, which is expected? I'm fine moving this report out of here for further discussion about the issues.