bind 9 goes rogue and revert zone information

[Raul Dias]

Hello,

I have a very strange behavior that I am failing to understand.

2 to 5 times a week, a named server revert back to a previous version os 
a master zone.
This happens during the night, usually around 20h EST.

This zone has a serial of 3017020401 (yes, I typo the 3 somewhere in the 
past).
When it reverts its zone information, it goes back to 3016060101.

I have updated, restarted the host, clean all cache and journal files, 
grep all files in the host for 3016060101 (just shows up in the logs).

So, I have no clue why, or how it is happening. Where does it get the 
old information.

I thought first about the serial, but it would have happened in the past 
too, right?  As it should be a 32bit unsigned integer, it shouldn't be a 
problem, IMHO.

Yet, when "dig domain -t SOA @server", it is there again.

The host is a debian Jessie and bind is 9.9.5, 1:9.9.5.dfsg-9+deb8u8 
more specifically.


Thanks for any direction.
-rsd