I'm just working on an 850Gx2 which I've updated to 6.47. Interface name selection and display appears to be borked in webfig.
Here is the Interfaces page showing vlans and customised names for the ethernet ports:
The addresses page shows unknown for vlan and openvpn interface names and the standard interface names for the physical interfaces and bridge.
Anywhere you find a dropdown list of interfaces it only shows the physical interfaces with the standard names, and the bridge, no vlan interfaces etc:
In winbox everything appears to be fine (also appears fine in the CLI):