Snmptrap Input Bug

hi all,

when i start the logstash , i got the warning as follows,

# /opt/logstash/bin/logstash -f /etc/logstash/conf.d/logstash-snmptrap.conf

Settings: Default filter workers: 1
Logstash startup completed
warning: overwriting old MIB name 'system'
warning: overwriting old MIB name 'sysDescr'
warning: overwriting old MIB name 'sysObjectID'
warning: overwriting old MIB name 'sysUpTime'
warning: overwriting old MIB name 'sysContact'
warning: overwriting old MIB name 'sysName'
warning: overwriting old MIB name 'sysLocation'
warning: overwriting old MIB name 'sysServices'
warning: overwriting old MIB name 'interfaces'
warning: overwriting old MIB name 'ifNumber'

what's mean about the warning ?

What does your config look like?
What version are you on?

logstash 2.1.3

my config ,

input {
snmptrap {
community => "public"
yamlmibdir => "/opt/logstash/vendor/bundle/jruby/1.9/gems/snmp-1.2.0/data/ruby/snmp/mib"
type => "snmptrap"
}
}