'Netlink: File exists' messages out of bird6

Hi all, I'm periodically seeing bird6 log these message (and get rate limited, which implies there were quite a few at once...) Nov 30 03:38:17 wlg-por-router2 bird6: Netlink: File exists Nov 30 03:38:17 wlg-por-router2 bird6: ... Any hints on how best to troubleshoot this? -- Michael