Invalid characters in source code

[lpar]

Clean install of Rails 3 on Ubuntu 10.04 LTS, using Ruby 1.9.3p194. System locale is UTF-8.

Installing ri documentation for journey-1.0.4...
unable to convert U+03B5 from UTF-8 to US-ASCII for lib/journey/nfa/dot.rb, skipping
unable to convert U+25CB from UTF-8 to US-ASCII for lib/journey/visitors.rb, skipping

Rdoc 3.9.4, RubyGems 1.8.23.

Validating the files with uconv -f UTF-8 :

$ uconv -f UTF-8 dot.rb 
Conversion from Unicode to codepage failed at input byte position 178. Unicode: 03b5 Error: Invalid character found
$ uconv -f UTF-8 visitors.rb 
Conversion from Unicode to codepage failed at input byte position 3233. Unicode: 25cb Error: Invalid character found

Both files claim to be UTF-8 at the top.