InvalidByteSequenceError: ""\xC3"" on US-ASCII

I am getting the following error in the logstash indexer (repeated many many times). I tried to explicitly set the encoding to utf-8, to no avail. Why is logstash using US-ASCII as encoding? That doesn't make sense, sounds like a bug in the code. Could it be a bug in the redis input plugin?

I tried it in git master, the problem is still there...

The string is correct utf-8, as I can see from python (sorry, I only know python, not ruby):

>>> print "CA Patronato de la Juventud Cat\xC3\xB3lica".decode("utf8")
CA Patronato de la Juventud Católica

{:timestamp=>"2013-11-12T13:54:05.847000+0000", :message=>"

{\"node\":\"0\",\"molly_customer\":\"apitest\",\"command_port\":\"7000\",\"type\":\"mollyapi.async\",\"message\":\"event:4:1384264442.839413:1384264443.030268:fb:2013-11-13,39597,21600:CA Patronato de la Juventud Cat\xC3\xB3lica:CA Belgrano de C\xC3\xB3rdoba:undefined:undefined:undefined::pre_event\",\"@timestamp\":\"2013-11-12T13:54:03.183Z\",\"@version\":\"1\",\"host\":\"10.122.82.81:49980\"}

", :exception=>#<Encoding::InvalidByteSequenceError: ""\xC3"" on US-ASCII>, :backtrace=>["org/jruby/RubyString.java:7596:in `encode'", "json/ext/Parser.java:175:in `initialize'", "json/ext/Parser.java:151:in `new'", "jar:file:/opt/logstash/logstash-1.2.3.dev-flatjar.jar!/META-INF/jruby.home/lib/ruby/1.9/json/common.rb:155:in `parse'", "file:/opt/logstash/logstash-1.2.3.dev-flatjar.jar!/logstash/codecs/json.rb:28:in `decode'", "file:/opt/logstash/logstash-1.2.3.dev-flatjar.jar!/logstash/inputs/redis.rb:129:in `queue_event'", "file:/opt/logstash/logstash-1.2.3.dev-flatjar.jar!/logstash/inputs/redis.rb:149:in `list_listener'", "file:/opt/logstash/logstash-1.2.3.dev-flatjar.jar!/logstash/inputs/redis.rb:225:in `listener_loop'", "file:/opt/logstash/logstash-1.2.3.dev-flatjar.jar!/logstash/inputs/redis.rb:241:in `run'", "file:/opt/logstash/logstash-1.2.3.dev-flatjar.jar!/logstash/pipeline.rb:155:in `inputworker'", "file:/opt/logstash/logstash-1.2.3.dev-flatjar.jar!/logstash/pipeline.rb:149:in `start_input'"], :level=>:error}