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:
system ~/projects/jruby $ jruby --1.9 -ryaml -e 'YAML.load("\ufffd".to_yaml)'
StreamReader.java:98:in `checkPrintable': unacceptable character '�' (0xFFFD) special characters are not allowed
in "<reader>", position 4
from StreamReader.java:191:in `update'
from StreamReader.java:63:in `<init>'
from PsychParser.java:115:in `parse'
from PsychParser$INVOKER$i$1$0$parse.gen:65535:in `call'
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.