VLCMP 1.1.11+ related
1.
Settings(extended) -> Input/Codecs -> Demuxer -> Playlist -> AutoRun
This setting affects both, a playlist double-click as well as a media file double-click.
Playlist -> AutoRun should only affect a playlist but not a media file.
2.
In addition to that I found the following behavior:
The '--no-playlist-enqueue' parameter within the registry's prog-id (e.g. vlc.mp3) command has no effect.
The item (e.g. mp3 song) will be added to the playlist anyway.
In total there should be 3 different functions:
--> Play normal (without adding to playlist) -> --started-from-file --no-playlist-enqueue
--> Play and Add to playlist---------------------> --started-from-file --playlist-enqueue
--> Add to playlist but do not play-------------> --playlist-enqueue