Massive Parse Tree Failure in Logstash 5.0.0-alpha3

00-Sample run.txt

# Example packet:
% echo -n '<123>Aug  4 07:54:35 foo bar: { "hello": "world" }' | nc -vu 127.0.0.1 9514

% bin/logstash --version
logstash 5.0.0-alpha4

% bin/logstash -f logstash-config-broken.conf
Pipeline main started
{
  "_data"                => {
    "hello" => "world"
  },
  "syslog_severity_code" => 3,
  "syslog_facility"      => "clock",
  "syslog_facility_code" => 15,
  "program"              => "bar",
  "message"              => "<123>Aug  4 07:54:35 foo bar: { \"hello\": \"world\" }",
  "type"                 => "syslog",
  "logsource"            => "foo",
  "content"              => "{ \"hello\": \"world\" }",
  "syslog_severity"      => "error",
  "tags"                 => [
    [0] "data",
    [1] "json"
  ],
  "@timestamp"           => 2016-08-04T14:59:46.981Z,
  "@version"             => "1",
  "host"                 => "127.0.0.1",
  "timestamp"            => "Aug  4 07:54:35"
}

logstash-config-broken.conf

input {
  udp {
    host => "127.0.0.1"
    port => 9514
    type => "syslog"
  }
}
filter {
  # This grok FAILS with a PARSE ERROR
  grok {
    match => { "message" => "<%{NONNEGINT:syslog_pri}>%{SYSLOGBASE} %{GREEDYDATA:content}" }
    add_tag => "grok"
  }
  if "grok" in [tags] {
    syslog_pri {}
  }
  mutate {
    remove_field => [ "syslog_pri" ]
    remove_tag   => [ "grok" ]
  }
}
filter {
  if [content] {
   json {
      target => "[_data]"
      source => "content"
      add_tag => [ "data", "json" ]
   }
  }
}
filter {
  if [program] == "ossec" and [_data] {
    if [_data][component]  {
       grok {
         match => { "[_data][component]" => "\(%{IPORHOST:src}\) %{WORD}->%{GREEDYDATA:src_file}" }
         add_tag => [ "ossec_valid" ]
       }
    }
  }
}
filter {
    mutate {
        remove_field => [ "_json" ]
    }
}
output {
   stdout {
     codec => "rubydebug"
   }
}