Inconsistent behavior between Lua 5.1 and LuaJit

nilortwelve.lua

function advise (adviceFn, ogFn) 
	return function (...) adviceFn(unpack(arg)) ogFn(unpack(arg)) end
end

function foo (x) 
	print ("foo") 
	print (x)
end

function bar (x) 
	print "bar" 
	print (x) 
end

function main ()
	foo = advise(foo,bar)
	print "working"
end

foo(12)
main()
foo(12)

Output:

 lua nilortwelve.lua
foo
12
working
foo
12
bar
12

luajit nilortwelve.lua 
foo
12
working
foo
nil
bar
nil

I admit, I'm stumped. Did I hit some undefined behavior?

NB: this is because arg is deprecated. use adviceFn(...) directly, or a, b = ... to dereference/unpack. Hat-tip Neffi on #lua freenode.