Dear Bart,

thank you for the hint. Indeed, I found an edit-command-line module in zshcontrib.
And yes, it is loaded by oh-my-zsh. So I could fix my theme script.

Unfortunately, I have no idea how to set the MODE variable the way you mentioned.
If anybody wants to tell me, you can find the script at 
  https://github.com/tannhuber/oh-my-zsh/blob/master/themes/budspencer.zsh-theme
But don't waste your time. Everything is working well, now.

Thank you
Joseph
Bart Schaefer <schaefer@brasslantern.com> schrieb am 3:50 Donnerstag, 15.Mai 2014:

On May 14,  9:18pm, Sepp Tannhuber wrote:
} Subject: vi-mode: editor function

}
} I have written a theme for the oh-my-zsh prompt from robbyrussel
} because I was sometimes confused about the different vi modes. My
} prompt shows, at a glance, which vi mode is active, similar to the vim
} airline plugin.
[...]
} Unfortunately I could not find something like vi-editor it in the
} zshzle manual. Has anybody an idea what I can use instead? Or what is
} the default vicmd for [v]?

There is no default binding for v in vicmd mode, so you are encountering
something installed for you by oh-my-zsh.  Most likely it is the user-
contributed edit-command-line widget (man zshcontrib).

If oh-my-zsh hasn't already pre-empted the zle-line-init, zle-line-finish,
and zle-keymap-select widgets, you might find it more effective to set the
MODE variable with those, rather than trying to override all the individual
widgets that might change mode.