As shown in the comments for
JRUBY-6200, JRuby's "Psych" wrapper around SnakeYAML can't handle some unicode characters. This may be a SnakeYAML bug, or something in YAML spec we don't know about:
I'm filing this because the original cases in
JRUBY-6200 are resolved, and this seems to be a separate issue that won't affect most people.