Prompt width miscomputed with conditional substring

[Bernie Innocenti <bernie@xxxxxxxxxxx>]

My zsh prompt is:

local ret_status="%(?:%{$fg_bold[green]%}%%:%{$fg_bold[red]%}%%%s)"
PROMPT="%{$fg[red]%}%n%{$reset_color%}@%{$fg[blue]%}%m:%{$fg[yellow]%}%~
%(1j,$fg[cyan][%j],)${ret_status}%{$reset_color%} "

When I have background jobs, the prompt becomes 3 characters longer and
command-line editing seems to wrap at the wrong column.

This is also reproducible with zsh built from git (zsh-5.0.7-374-gd4f50f2).

-- 
 _ // Bernie Innocenti
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