Yes, I was very surprised this behavior :)
And i was helped by [a coment](https://github.com/rubinius/rubinius/blob/3c191e31d06b1f1a2082de14dbcdd8ecd306f714/kernel/common/array19.rb#L216-L218)  from [non updated version guard in spec](https://github.com/rubyspec/rubyspec/commit/157fe7751b802a4347e416d40ff5a15071fdea4e)

But this is my problem, you are right !