[dnsdist] weird cached behavior

[Nico]

I need some help, if posible, to understand some strange situation.
Unfortunately we can give a method to reproduce it, but we have some hard
data.

We have a couple of dnsdist servers. Half 1.1.0 and half 1.3.2, moving from
old to new.
The 1.1.0 are still getting most of the traffic and the problem happens
there.
The user base is 100% mobile, and we serve more than 200kqps

We received complains about domain names unresolved which do exist.
first time, ignored, second time some checks, third time more checks.
The problem gets solved expunging the cache.

All fine BUT, during our checks we noticed inconsistent behavior of the
cache regarding this names.
Android chrome access to page ->  fails.
AndroDNS (dns tools) query standard ->  empty answer
               query over TCP -> correct answer
               query whith DO -> correct answer
               query whith CD -> correct answer
Checking from Linux:
host command: -> empty answer
        host over TCP -> correct answer
dig command -> correcto

When the cache is cleared, all works OK.
We asume that there is some situation with the domain which create wrong
cached entries,
but why we have different answers from UDP than from TCP?
the query flags are exactly the same (0x0100)

And why the difference between host and dig (the only difference at paquet
level is the AD bit set on DIG, 0x0100 vs 0x0120)


If anybody can help a little.....

Thanks!!
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