problem with both-faiover-server updating the DNS

[gnafou]

Hello 
I currently have  isc dhcp servers working with failover and dns update ( interim style ) 
When upgrading my debian machine from wheezy to jessie, it upgraded as well dhcpd from 4.2.2 to 4.3.1.
Since i have upgraded, i find some weird behaviour with the DNS-Update :
for some of the machines, both  dhcp servers answer, then they both update  the DNS.
I do not have any log lines stating ' lease owned by peer' 
And after the lease is over,  one of the dhcp server  deletes the dns map though the machine is currently being served by the other server.
thank you if you can give me a hint 
Fred 
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