Problems with text/csv Content-Encoding = UTF-8 in Ruby Mechanize

Problems with text/csv Content-Encoding = UTF-8 in Ruby Mechanize

When attempting to load a page which is a CSV that has encoding of UTF-8,
using Mechanize V2.5.1, I used the following code:
a.content_encoding_hooks << lambda{|httpagent, uri, response, body_io|
response['Content-Encoding'] = 'none' if
response['Content-Encoding'].to_s == 'UTF-8'
}
p4 = a.get(redirect_url, nil, ['accept-encoding' => 'UTF-8'])
but I find that the content encoding hook is not being called and I get
the following error and traceback:
/Users/jackrg/.rbenv/versions/1.9.2-p290/lib/ruby/gems/1.9.1/gems/mechanize-2.5.1/lib/mechanize/http/agent.rb:787:in
'response_content_encoding': unsupported content-encoding: UTF-8
(Mechanize::Error) from
/Users/jackrg/.rbenv/versions/1.9.2-p290/lib/ruby/gems/1.9.1/gems/mechanize-2.5.1/lib/mechanize/http/agent.rb:274:in
'fetch' from
/Users/jackrg/.rbenv/versions/1.9.2-p290/lib/ruby/gems/1.9.1/gems/mechanize-2.5.1/lib/mechanize/http/agent.rb:949:in
'response_redirect' from
/Users/jackrg/.rbenv/versions/1.9.2-p290/lib/ruby/gems/1.9.1/gems/mechanize-2.5.1/lib/mechanize/http/agent.rb:299:in
'fetch' from
/Users/jackrg/.rbenv/versions/1.9.2-p290/lib/ruby/gems/1.9.1/gems/mechanize-2.5.1/lib/mechanize/http/agent.rb:949:in
'response_redirect' from
/Users/jackrg/.rbenv/versions/1.9.2-p290/lib/ruby/gems/1.9.1/gems/mechanize-2.5.1/lib/mechanize/http/agent.rb:299:in
'fetch' from
/Users/jackrg/.rbenv/versions/1.9.2-p290/lib/ruby/gems/1.9.1/gems/mechanize-2.5.1/lib/mechanize.rb:407:in
'get' from prototype/test1.rb:307:in `'
Does anyone have an idea why the content hook code is not firing and why I
am getting the error?