lua-zmq inverted pub-sub problem

console.log

# Spawn receiver 1
$ lua receiver.lua &
[1] 9728

R	9728	init
R	9728	create socket
R	9728	bind socket
R	9728	subscribe
R	9728	before receive msg loop

# Spawn receiver 2
$ lua receiver.lua &
[2] 9735

R	9735	init
R	9735	create socket
R	9735	bind socket
R	9735	subscribe
R	9735	before receive msg loop

# Spawn receiver 3
$ lua receiver.lua &
[3] 9739

R	9739	init
R	9739	create socket
R	9739	bind socket
R	9739	subscribe
R	9739	before receive msg loop

# Spawn sender
$ lua sender.lua 
S	9755	init
S	9755	create socket
S	9755	connect socket
S	9755	sending	MSG 1
S	9755	sending	MSG 2
S	9755	sending	MSG 3
S	9755	close
S	9755	term
R	9739	recieved	MSG 1	nil
R	9739	recieved	MSG 2	nil
R	9739	recieved	MSG 3	nil
R	9739	close
R	9739	term
S	9755	done
R	9739	done
[3]+  Done                    lua receiver.lua

# Spawn sender again
$ lua sender.lua 
S	9759	init
S	9759	create socket
S	9759	connect socket
S	9759	sending	MSG 1
S	9759	sending	MSG 2
S	9759	sending	MSG 3
S	9759	close
S	9759	term

# Sender hangs

receiver.lua

local posix = require 'posix'
local zmq = require 'zmq'

local old_print = print
local print = function(...)
  print("R", posix.getpid("pid"), ...)
end

print("init")
local context = assert(zmq.init(1))

print("create socket")
local conn = assert(context:socket(zmq.SUB))

print("bind socket")
assert(conn:bind("ipc://tmp.ipc"))

print("subscribe")
assert(conn:setopt(zmq.SUBSCRIBE, ""))

print("before receive msg loop")
for i = 1, 3 do
  print("recieved", conn:recv())
end

print("close")
conn:close()
conn = nil

print("term")
context:term()
context = nil

print("done")

sender.lua

local posix = require 'posix'
local zmq = require 'zmq'

local old_print = print
local print = function(...)
  print("S", posix.getpid("pid"), ...)
end

print("init")
local context = assert(zmq.init(1))

print("create socket")
local conn = assert(context:socket(zmq.PUB))

print("connect socket")
assert(conn:connect("ipc://tmp.ipc"))

for i = 1, 3 do
  local msg = "MSG " .. i
  print("sending", msg)
  assert(conn:send(msg))
end

print("close")
conn:close()
conn = nil

print("term")
context:term()
context = nil

print("done")