Keyword rest argument processing is inconsistent

0.output

$ ruby -v keyword_gotcha.rb
ruby 2.2.0dev (2014-06-05 trunk 46353) [x86_64-darwin13]
1
{:b=>2}
{:b=>2}
1
{}
{:gotcha=>1}

keyword_gotcha.rb

def m(a: 1, **kw)
  p a, kw
  kw[:gotcha] = 1
end

h = {b: 2}
m h
p h

h = {}
m h
p h