GnuPG 2.1 with Git, problem in zsh, not in ksh

[Andreas Kusalananda Kähäri <andreas.kahari@xxxxxxx>]

Hi,

I'm a Perl developer using zsh and git, and I sign my git commits using
gpg2 (from GnuPG 2.1).

In ksh, I'm able to "git commit -S code.pl", but I noticed that this
stopped working the other week when I started using zsh:

[laptop] ENA % git commit -S submit.pl
gpg: signing failed: Inappropriate ioctl for device
gpg: signing failed: Inappropriate ioctl for device
error: gpg failed to sign the data
fatal: failed to write commit object

Simply starting up ksh and running the same command works. "Works"
in this case means git calls gpg2 which uses pinentry to request the
password, etc.

Since I'm resonably new to zsh, I'm not even sure where to start looking
for the solution.  The environment variables in zsh are identical to
those in ksh.

This is my ~/.zshrc file:

# For interactive zsh sessions

# Completion options
unsetopt AUTO_REMOVE_SLASH

# History options
setopt EXTENDED_HISTORY
setopt HIST_EXPIRE_DUPS_FIRST
setopt HIST_FIND_NO_DUPS
setopt HIST_IGNORE_DUPS
setopt SHARE_HISTORY
unsetopt INC_APPEND_HISTORY

HISTFILE="$HOME/.zsh/history"
HISTSIZE=10000
SAVEHIST=5000

bindkey '^R' history-incremental-pattern-search-backward
bindkey '^G' history-beginning-search-backward

# Input/Output options
setopt CORRECT
setopt DVORAK

# Job control options
setopt BGNICE

# Prompting options
#setopt TRANSIENT_RPROMPT

PROMPT="[%m] %B%F{red}%1~%f%b %# "
RPROMPT="%F{blue}%T%f"

# Zle options
unsetopt BEEP
setopt VI

autoload -Uz compinit
compinit

alias ls="ls -F"

export VISUAL="vim"
export EDITOR="$VISUAL"

-- 
:: Andreas Kusalananda Kähäri, Bioinformatics Developer, BILS,
:: Uppsala University, Sweden
::----------------------------------------------------------------------
:: My other car is a cdr.