live_loop can't control surrounding with_fx

[emlyn]

Previously posted here https://groups.google.com/forum/#!topic/sonic-pi/aLI4MGLnzA4
I'm not sure if this is a bug, expected behaviour, or something I'm doing wrong, but in any case it is quite confusing. If I have a piece of code with a live_loop inside a with_fx, like the following:

with_fx :reverb do |fx|
  live_loop :test do
    play :c
    sleep 1
  end
end

If I run it at least once, then I modify the loop to control the fx, for example:

with_fx :reverb do |fx|
  live_loop :test do
    control fx, amp: 0
    play :c
    sleep 1
  end
end

It doesn't have any effect on the sound. I can work around it by moving the fx inside the live_loop, but I believe that is less efficient because it creates a new fx node every time it goes around the loop.

[rbnpi]

See Some Question About Threads by J L Diaz in Sonic Pi Google Group where this is discussed and he suggests a work around on how to do it.