Here is the rubyforge ticket :
http://rubyforge.org/tracker/?func=detail&aid=15425&group_id=426&atid=1698

The participating people have been quite far but at this stage, we
would need somebody from the core to help us fix the problem. Please !

The problem is related to magic local vars like $? which don't get
collected if no regular local var has been promoted.

def leak
  "x" =~ //
end

def no_leak
  y = "x"
  y =~ //
end

-- 
Cheers,
  zimbatm