Ruby babel src block does not run some code

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For example, I have a ruby src block like this:

```
#+BEGIN_SRC ruby
  module A
    CREF = "*** CREF in module A"
  end

  module A
    module B
      puts CREF
    end
  end
#+END_SRC
```

And press `[C-c C-c]` to execute, get this error:
```
#+BEGIN_EXAMPLE
-:3: module definition in method body
-:4: dynamic constant assignment
  CREF = "*** CREF in module A"
        ^
-:7: module definition in method body
-:8: module definition in method body
#+END_EXAMPLE
```

My emacs version: 24.5.1
My org-mode version: 8.3.4 (installed from MELPA)

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IRC(freeenode): stardiviner                     Twitter:  @numbchild
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Blog: http://stardiviner.github.io/

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