frontend does not support selecting main interfaces

The server side of Zabbix has been written with a single main interface and multiple non-main interfaces in mind. Currently, all created interfaces are main. While the frontend side has its own way of deciding, for instance, which interfaces to link template items to, server might or might not work as expected until main interfaces are implemented properly in the frontend.

Specification: http://zabbix.org/wiki/Docs/specs/ZBX-3527