Syslog to IPv6 Server

I'm trying to send syslog messages from a fortigate (v6.2.3) to a local syslog server using ipv6.  I have ipv6 connectivity confirmed between the fortigate and the syslog server on the same network segment.  When I assign the syslog server's ipv6 address in the "Send logs to syslog" setting on the fortigate, the syslog messages do not reach the syslog server (confirmed via wireshark).  If I switch that ipv6 address to the ipv4 address of the syslog server the message begin showing up at the syslog server.  

I am wondering if I can only achieve this by first sending the syslog log messages to a Fortianalyzer rather than directly from the fortigate?  I thought the Fortigate was supposed to be able to handle this, maybe I'm missing something?