Logtash Error

There's this error I am getting ever since I moved to Logstash 2.3.1.

logstash-current/vendor/bundle/jruby/1.9/gems/mail-2.6.3/lib/mail/network/delivery_methods/sendmail.rb:72 warning: unsupported popen option: err

I keep getting a string of these. What is exactly causing this?

Thanks

Seems to be a bug. Perhaps you can use SMTP instead?