[Samba] DNS returns a wrong ip address

[Peter Boos]

We got two samba DC's with DNS, managed by a windows system with admin tools installed.
If I ping a certain client a testing system it does return on a wrong IP (and then fails ping).
The returned IP is  192.168.99.21 while we use a 172.x.x.x network
It returns a dual host reply but 192 first 172 next, I checked both DNS systems from Windows side.
Also NSlookup on Linux

The entry is not visible on the windows system with admin tools.
Even when I removed the proper available entry, a nslookup resulted in an wrong answer.
When I tried a wins lookup nmblookup it cannot resolve it either, so I don't know where it comes from.
There are no other DNS's servers involved then just the two we have. 
Like its not a forward lookup result on pfsense or so, we don't do DNS there.
Just for the record; the samba systems are headless systems.

Any ideas on how to resolve this DNS conflict?