Calling Fiber.yield in a constructor results in can't cross C function boundary exception. Could this be classified as an error considering the fact that only pure ruby code is involved?

Steps to reproduce:

1. run the following code using mruby

class C
  def initialize
    Fiber.yield(1)
  end
end
fiber = Fiber.new do
  C.new
end
fiber.resume

see also: h2o/h2o#1536; relates to #3056