mongrel ri is not installing

when i execute
$~ sudo gem install mongrel

Building native extensions. This could take a while...
Successfully installed mongrel-1.1.4
1 gem installed
Installing ri documentation for mongrel-1.1.4...
ERROR: While generating documentation for mongrel-1.1.4
... MESSAGE: Unhandled special: Special: type=33, text="A"
... RDOC args: --ri --op /usr/lib/ruby/gems/1.8/doc/mongrel-1.1.4/ri
--quiet lib ext
(continuing with the rest of the installation)
Installing RDoc documentation for mongrel-1.1.4...

what is the error for ri doc ?