yaml.rb produces YAML it can't parse from Sets of Hashes

[whateley]

I'm producing YAML that contains multiple Sets, each of which may contain the same instance of a Hash. to_yaml works, but YAML.load says the result has got a syntax error.

Here's a test program:

require "set"
require "yaml"

# it only seems to occur with hashes
b = { "z" => 2 }

# the Sets must be two different instances
s1 = Set.new([b])
s2 = s1.dup

yaml = [s1,s2].to_yaml

YAML.load(yaml)

And here's the output:

/usr/lib/ruby/1.8/yaml.rb:133:in `load': syntax error on line 4, col -1: `      z: 2 (ArgumentError)
    : true

- !ruby/object:Set 
  hash: 
    *id001: true
'	from /usr/lib/ruby/1.8/yaml.rb:133:in `load'
	from /home/therion/test.rb:14

This is on ruby 1.8.5 (2006-12-04 patchlevel 2) [i686-linux]