Rails - Nov 2006 - headers[''Content-Type''] & link_to_remote on Rails Edge

I''m on rails edge and am calling an after filter on my actions. Works  
except for my ajax calls via link_to_remote. When I inspect headers,  
I see the ''Content-Type'' is key for an object rather than a
string.
Shouldn''t it be a string? Anyone know if this is a bug or if
I''m
dealing with this incorrectly.

Thanks,

Jamie

The code:
   after_filter :set_charset
   def set_charset
     logger.debug("!!!!---- headers: #{headers.inspect}")
     unless headers[''Content-Type''] =~ /charset/i
       headers[''Content-Type''] ||= "text/html"
       headers[''Content-Type''] += '';
charset=utf-8''
     end
     headers[''Pragma''] = ''no-cache''
     headers[''Cache-Control''] = ''no-cache, no-store,
must-revalidate''
   end

from the logger:
!!!!---- headers: {"Status"=>"200 OK",
"cookie"=>[],
"Content-Type"=>#<Mime::Type:0x1316954
@synonyms=["application/javascript",
"application/x-javascript"],
@symbol=:js, @string="text/javascript">,
"Cache-Control"=>"no-cache"}

Part of the stack trace:

NoMethodError (undefined method `+'' for #<Mime::Type:0x1316954>):
     /app/controllers/application.rb:87:in `set_charset''
     .//vendor/rails/actionpack/lib/action_controller/filters.rb: 
471:in `call''
     .//vendor/rails/actionpack/lib/action_controller/filters.rb: 
465:in `call''
     .//vendor/rails/actionpack/lib/action_controller/filters.rb: 
633:in `call_filter''
     .//vendor/rails/actionpack/lib/action_controller/filters.rb: 
615:in `perform_action_without_benchmark''
     .//vendor/rails/actionpack/lib/action_controller/benchmarking.rb: 
66:in `perform_action_without_rescue''