Argument destructuring fails when the argument shadows a local in the containing scope

[brixen]

Given the following code:

def m
  yield [[1,2], [3,4]]
end

def n(b)
  m do |(b, c)|
    p b, c
  end
end

n 5

The output on Rubinius 1.9 mode is:

5
nil

while the expected output is:

[1, 2]
[3, 4]

The correct output is produced by Rubinius if the destructuring is removed from the block arguments or the parameter to #n is changed so that it is not shadowed by the block argument.