Heroku console giving Encoding::UndefinedConversionError - ruby-on-rails-3

Question

Running a heroku console with
heroku run console
all commands returning UTF-8 characters (like german Umlauts) will result in the following error:
irb(main):004:0> Play.all[-2]
Play Load (27.5ms) SELECT "plays".* FROM "plays" ORDER BY name asc
Encoding::UndefinedConversionError: U+00E4 from UTF-8 to US-ASCII
from /usr/local/lib/ruby/1.9.1/irb.rb:311:in `write'
from /usr/local/lib/ruby/1.9.1/irb.rb:311:in `printf'
from /usr/local/lib/ruby/1.9.1/irb.rb:311:in `output_value'
from /usr/local/lib/ruby/1.9.1/irb.rb:160:in `block (2 levels) in eval_input'
from /usr/local/lib/ruby/1.9.1/irb.rb:273:in `signal_status'
from /usr/local/lib/ruby/1.9.1/irb.rb:156:in `block in eval_input'
from /usr/local/lib/ruby/1.9.1/irb/ruby-lex.rb:243:in `block (2 levels) in each_top_level_statement'
from /usr/local/lib/ruby/1.9.1/irb/ruby-lex.rb:229:in `loop'
from /usr/local/lib/ruby/1.9.1/irb/ruby-lex.rb:229:in `block in each_top_level_statement'
from /usr/local/lib/ruby/1.9.1/irb/ruby-lex.rb:228:in `catch'
from /usr/local/lib/ruby/1.9.1/irb/ruby-lex.rb:228:in `each_top_level_statement'
from /usr/local/lib/ruby/1.9.1/irb.rb:155:in `eval_input'
from /usr/local/lib/ruby/1.9.1/irb.rb:70:in `block in start'
from /usr/local/lib/ruby/1.9.1/irb.rb:69:in `catch'
from /usr/local/lib/ruby/1.9.1/irb.rb:69:in `start'
from /app/vendor/bundle/ruby/1.9.1/gems/railties-3.2.12/lib/rails/commands/console.rb:47:in `start'
from /app/vendor/bundle/ruby/1.9.1/gems/railties-3.2.12/lib/rails/commands/console.rb:8:in `start'
from /app/vendor/bundle/ruby/1.9.1/gems/railties-3.2.12/lib/rails/commands.rb:41:in `<top (required)>'
from script/rails:6:in `require'
from script/rails:6:in `<main>'Maybe IRB bug!!
I do not really understand the cause of this.
Is there a workaround?
I am using iTerm with a setting of "UTF-8 xterm-color".
Update
This error completely disappeared for no reason known to me and I can reproduce it neither under ruby 1.9.2p320 nor 1.9.3p448
Typing "\u00E4" into the console now yields "ä" as expected:
irb(main):001:0> "\u00E4"
=> "ä"