After using the command
dopusrt /col import /create /nocheck /clear /utf16le "Imported" "C:\Playlist.m3u", trying to delete the
#EXTM3U item that was added to the collection was not possible, either with
Delete SHIFT or
Delete REMOVECOLLECTION. The error message was "An unknown error ocurred".
Deleting other invalid items with proper path was okay.
Maybe strings that aren't a proper path should not be imported?