double server.register causing telnet server 'help'-problem

test.liq:

set("server.telnet", 4)
set("server.telnet.port", 4321)
server.register("l", fun(x) -> "BOOM")
server.register("l", fun(x) -> "BOOM")
output.dummy(blank())

start it and connect to 4321 port with telnet:
$ liquidsoap test.liq

$ telnet localhost 4321
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.

try to get help:
help
ERROR: Invalid_argument("equal: functional value")
END