KSH switches editin modes when cycling through history. Why?

Hello all,
Working in KSH using Solaris, the default editor is VIM. So, per session, I run a small rc script which calls

export editor=emacs

This works for commands at the prompt. But if I cycle through command history (Using the up arrow) the command line editor defaults to VIM. How can I tell Korn that I want to use emacs as the default command-line editor in this situation?

set -o emacs

aha! Very good. Thanks