rubygems not working with ruby 2.2?

[Koichiro IWAO]

Hello,

I switched ruby version 2.1 -> 2.2 but rubygems seem not working.
I performed upgrade like ports/UPDATING 20141008.

Writing make.conf.
DEFAULT_VERSIONS= ruby=2.2

and then
portmaster -o lang/ruby22 lang/ruby21 # successfully finished
portmaster -R -r ruby-2.2 # failed with following message

===>  Configuring for rubygem-activesupport-3.2.19
===>  Building for rubygem-activesupport-3.2.19
/usr/local/lib/ruby/site_ruby/2.2/rubygems/specification.rb:1960:in 
`block (2 levels) in to_yaml': stack level too deep (SystemStackError)
         from /usr/local/lib/ruby/2.2/psych/coder.rb:36:in `map'
         from 
/usr/local/lib/ruby/site_ruby/2.2/rubygems/specification.rb:1959:in 
`block in to_yaml'
         from /usr/local/lib/ruby/2.2/psych/deprecated.rb:19:in `call'
         from /usr/local/lib/ruby/2.2/psych/deprecated.rb:19:in `block in 
quick_emit'
         from 
/usr/local/lib/ruby/site_ruby/2.2/rubygems/specification.rb:1960:in 
`block (2 levels) in to_yaml'
         from /usr/local/lib/ruby/2.2/psych/coder.rb:36:in `map'
         from 
/usr/local/lib/ruby/site_ruby/2.2/rubygems/specification.rb:1959:in 
`block in to_yaml'
         from /usr/local/lib/ruby/2.2/psych/deprecated.rb:19:in `call'
          ... 9619 levels...
         from 
/usr/local/lib/ruby/site_ruby/2.2/rubygems/command_manager.rb:147:in 
`process_args'
         from 
/usr/local/lib/ruby/site_ruby/2.2/rubygems/command_manager.rb:117:in 
`run'
         from 
/usr/local/lib/ruby/site_ruby/2.2/rubygems/gem_runner.rb:65:in `run'
         from /usr/local/bin/gem22:30:in `<main>'
===> Compilation failed unexpectedly.
Try to set MAKE_JOBS_UNSAFE=yes and rebuild before reporting the failure 
to
the maintainer.
*** Error code 1

Any ideas?
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