zsh command line searching does not echo searched string

Issue

When zsh is used in ksh emulation mode with vi mode enabled, command line searching does not echo the search string.

$ ls -l /usr/bin/ksh
lrwxrwxrwx 1 root root 8 Jul  8 10:36 /usr/bin/ksh -> /bin/zsh
$ ksh
$ set -o vi

At this stage using <esc>+/ to search the history will work although the searched string will not appear on the screen.