[CentOS] Pipe into logger duplicates messages in /var/log/messages

I am trying to pipe the output from a process into syslog using the logger
command. Initially I pipe the output into a separate file, but as it 
happens
this filled up the disk when things went wrong. So I figured I redirect the
output to syslog and let logrotate deal with the roll-over and archive 
of the
file.

However the following command :

echo "HI" > logger -t test

Resulted in the message appearing twice in /var/log/messages on my CentOS 6
system. I tested it on Gentoo as well where it behaved correctly, only 
showing
a single message.

Any pointers on why CentOS duplicates these messages.

Alex