DNS records not updated ?

Hi,
our company is running Windows 2003 Active Directory, some clients having same IP address on DNS.

example : when ping client A, getting IP address 128.1.8.30, but when VNC to A will go to client B, ping client B will get same IP address as client A.

any reason why ?, we are having DNS/DHCP/WINS integrated with AD running on one Domain Controller