Still incompatible character encodings: ASCII-8BIT and UTF-8

My environment is:
jruby 1.6.7 (ruby-1.9.2-p312) (2012-02-22 3e82bc8) (OpenJDK 64-Bit
Server VM 1.6.0_24) [linux-amd64-java] and rails 3.2.2.

In my config/application.rb I have:
config.i18n.default_locale = :it
config.encoding = “utf-8”

in my show view I have:

= number_to_currency(@classification.amount)

it display something like this: 516.000,00 €, with the euro symbol.
If I click “link_to t(‘Show’), company”, I see the company details
with no problem and I see the euro symbol too.
But if I try to update the company, when it render the show view it
says:
incompatible character encodings: ASCII-8BIT and UTF-8.
I don’t understand why.

I’ve opened a bug in jiira.