Domain Controller pointing host IP to another site

Hi All

I have 3 site in my company

1. Site A 

    Domain controller ip 192.168.1.5.

    Client Subnet 192.168.1.0/24, 192.168.6.0/24, 192.168.8.0/24

2. Site B

    Domain Controller ip 192.168.14.5 (Holding FSMO)

    Client Subnet 192.168.14.0/24, 192.168.2.0/24

3. Site C

    Domain Controller 192.168.15.5

     Client Subnet 192.168.15.0/24

Im creating A record in dns as per below 

- webmail.mydomain.com with IP 192.168.1.2

- webmail.mydomain.com with IP 192.168.14.2

- webmail.mydomain.com with IP 192.168.15.2

In all dns server round robin feature disable.

We found from our client in site A ping to webmail going to ip 192.168.14.2 sometime going to 192.168.15.2 also from our Domain server when ping to webmail it also going to same ip like testing in user. try to ipconfig /flushdns & ipconfig /registerdns its work try ping than going to 192.168.1.2 but it only work for a hour than it will back again to other said.

Anyone got idea to solve this

Thanks

Ibnu