I have the same problem as this thread https://supportforums.cisco.com/thread/2175196.
On WiFi my SPLIT-Tunnel VPN works perfectly and all SPLIT-DNS requests are sent to my DNS servers.
However on celullar connections (I'm using TMobile) when using safari the VPN is established however the carrier DNS response is being used.
In the above thread a fix wasn't suggested. Any ideas how to fix this?