There are lots of posts about this, including an acknowledgement from Sling that is their fault, but they cannot do anything about it. See https://community.sling.com/message/43234#43234
It appears that if you specify Scientific Atlanta as the manufacturer of your device then Comcast have insisted that their remote skin is displayed. I know nothing of the background politics of this apparently arrogant stance by Comcast, but Sling appeared to have bowed to the pressure done as they were told.
The solution should be to re-run the Video Sources setup and make sure that you specifiy Time Warner as the Manufacturer. That seems to have worked for everyone else, so give it a try.