Undefined method `to_sym' for #<YAML::Syck::MergeKey

I have a stock gentoo rails install. I get something like this when I
try to use script/generate, rake migrate or script/console and probably

0 wicked www/sharkwatch % ./script/console
Loading development environment.

symbolize_keys':NoMethodError: undefined methodto_sym’ for

to_sym is indeed not defined in /usr/lib/ruby/1.8/yaml.rb or

What’s going on here?