Bug in dhclient, isc_named or misconfiguration ?

Hi group,

Recently i come up with this problem: running isc_named + dhclient cause isc_named to periodically loose binding to TCP port:

Sep 7 13:45:02 ns dhclient[12533]: DHCPREQUEST on vio0 to 169.254.169.254
Sep 7 13:45:02 ns dhclient[12533]: DHCPACK from 169.254.169.254 (fe:00:00:88:fe:63)
Sep 7 13:45:02 ns named[76593]: no longer listening on XXX.XXX.XXX.XXX#53
Sep 7 13:45:02 ns named[76593]: listening on IPv4 interface vio0, XXX.XXX.XXX.XXX#53
Sep 7 13:45:02 ns named[76593]: binding TCP socket: address in use
Sep 7 13:45:02 ns dhclient[12533]: bound to XXX.XXX.XXX.XXX -- renewal in 40027 seconds.

XXX is redacted public IP.

This is OpenBSD 6.1
In bind i have already configured interface-interval 0; - but this do not fix problem, any idea ? This problem looks like isolated to OpenBSD.

Thanks,

_
Zbyszek Żółkiewski