DNS not working in windows enviroment

Several different versions of OSX from 10.5 to 10.10.3 on macbooks, macminis, imacs. Running in a primarily windows enviroment on wired ethernet. For network settings we use DHCP. Verified that the DNS servers are the same as the ones shown on the windows machines. Before a couple of weeks ago, we were able to connect to windows machines using remote desktop and specifying the name of the window machine as in sta-43567.our.domain . We were able from a mac computer to ping sta-43567.our.domain and get a response. Something changed in the network configuration and now the macs have lost the ability to ping the windows stations. The response from the ping command is "computer not found". We can still ping 'official' share computers such as file-server-1.our.domain . The "interesting" part is that when pinging the same computer name from a windows machine there is a response like

2002:abab:043f::043f:abab . Also connecting using remote desktop from a windows computer works. I guess this is an IPV6 address, but there is also an IPv4 address which can be seen by windows machines if we use the command "ping -4 " which i guess forces the windows ping command to use IPV4. The thing i cannot understand is why the OSX computers cannot resolve the computer name, while the windows machines can.

Does anyone have any idea why this might be happening?

Thank you in advance

Costas