Psych::SyntaxError while installing some gems in 1.9 mode

$ jruby -v; jruby -S gem install gherkin                                                                     system master a9a50e0
jruby 1.7.0.dev (ruby-1.9.3-p28) (2012-01-31 a9a50e0) (Java HotSpot(TM) 64-Bit Server VM 1.6.0_29) [darwin-x86_64-java]
Psych::SyntaxError: special characters are not allowed
                             parse at org/jruby/ext/psych/PsychParser.java:286
                      parse_stream at /usr/local/jruby/lib/ruby/1.9/psych.rb:154
                             parse at /usr/local/jruby/lib/ruby/1.9/psych.rb:125
                              load at /usr/local/jruby/lib/ruby/1.9/psych.rb:112
                         from_yaml at /usr/local/jruby/lib/ruby/shared/rubygems/specification.rb:490
                      load_gemspec at /usr/local/jruby/lib/ruby/shared/rubygems/package/tar_input.rb:195
                        initialize at /usr/local/jruby/lib/ruby/shared/rubygems/package/tar_input.rb:60
                              each at /usr/local/jruby/lib/ruby/shared/rubygems/package/tar_reader.rb:64
                              loop at org/jruby/RubyKernel.java:1336
                              each at /usr/local/jruby/lib/ruby/shared/rubygems/package/tar_reader.rb:55
                        initialize at /usr/local/jruby/lib/ruby/shared/rubygems/package/tar_input.rb:35
                              open at /usr/local/jruby/lib/ruby/shared/rubygems/package/tar_input.rb:20
                              open at /usr/local/jruby/lib/ruby/shared/rubygems/package.rb:44
                           from_io at /usr/local/jruby/lib/ruby/shared/rubygems/format.rb:62
                 from_file_by_path at /usr/local/jruby/lib/ruby/shared/rubygems/format.rb:46
                              open at org/jruby/RubyIO.java:1139
                              open at org/jruby/RubyKernel.java:295
                 from_file_by_path at /usr/local/jruby/lib/ruby/shared/rubygems/format.rb:45
                            format at /usr/local/jruby/lib/ruby/shared/rubygems/installer.rb:119
                              spec at /usr/local/jruby/lib/ruby/shared/rubygems/installer.rb:129
  ensure_required_ruby_version_met at /usr/local/jruby/lib/ruby/shared/rubygems/installer.rb:386
                           install at /usr/local/jruby/lib/ruby/shared/rubygems/installer.rb:156
                           install at /usr/local/jruby/lib/ruby/shared/rubygems/dependency_installer.rb:297
                              each at org/jruby/RubyArray.java:1609
                   each_with_index at org/jruby/RubyEnumerable.java:933
                           install at /usr/local/jruby/lib/ruby/shared/rubygems/dependency_installer.rb:270
                           execute at /usr/local/jruby/lib/ruby/shared/rubygems/commands/install_command.rb:121
                              each at org/jruby/RubyArray.java:1609
                           execute at /usr/local/jruby/lib/ruby/shared/rubygems/commands/install_command.rb:115
                            invoke at /usr/local/jruby/lib/ruby/shared/rubygems/command.rb:278
                      process_args at /usr/local/jruby/lib/ruby/shared/rubygems/command_manager.rb:147
                               run at /usr/local/jruby/lib/ruby/shared/rubygems/command_manager.rb:117
                               run at /usr/local/jruby/lib/ruby/shared/rubygems/gem_runner.rb:65
                            (root) at /usr/local/jruby/bin/gem:21