volume levels jumping when skipping a track

#!/usr/bin/liquidsoap

set("log.stdout", true);
set("server.telnet", true);

# is skipped flag
track.isSkipped = ref false;

# transition func
def transition(from, to)=
    if (!track.isSkipped) then
        track.isSkipped := false;
        add([fade.initial(to), fade.final(from)]);
    else
        add(normalize = false, [to, from]);
    end
end

# extended crossfade
def crossfade.switch(~id = "", ~conservative = true, ~start_next = 10., ~fade_in = 5., ~fade_out = 5., s)
  # i've tried to remove following two lines - but there were no effect (volume levels were still jumping)
  s = fade.in(duration = fade_in, s);
  s = fade.out(duration = fade_out, s);
  cross(id = id, conservative = conservative, duration = start_next, transition, s);
end

# security track
security = single("/home/security.mp3");

# external script just returns random track from folder
# add your script name here
playlist = request.dynamic(conservative = true, fun () -> request.create(list.hd(get_process_lines("external script"))))

# apply crossfade (we need it really only for tracks in playlist)
playlist = crossfade.switch(playlist);

# create main source
radio    = fallback(track_sensitive = false, [playlist, security]);

# output source
output.icecast(mount = "testme", host = "localhost", port = 80, password = "hackme", %mp3, radio)

# Updates program timeout, server command
def server.source.skip(unused) =
  track.isSkipped := true;
  source.skip(radio);
  "done"
end

# Register server command
server.register(namespace = "source",
  description = "Skips current track",
  usage = "skip", "skip", server.source.skip);