Bug#1052451: openssh-client: Ctrl-C kills ssh but not ssh-add, which steals input from the terminal

Package: openssh-client
Version: 1:9.4p1-1
Severity: important

It seems that that ssh command runs ssh-add automatically.
While I did a Ctrl-C to interrupt ssh started by unison (for
synchronization with a remote machine) from mutt, ssh-add is
still running and attached to the terminal:

UID          PID    PPID  C STIME TTY          TIME CMD
vlefevre    2129    2128  0 11:00 pts/5    00:00:04 mutt
vlefevre    2358       1  0 11:03 pts/5    00:00:00 ssh-add [...]

and it steals input (typed keys) that should go to mutt.

Note: ssh-add was asking for a passphrase, and I did not want to
enter it now. That's why I did Ctrl-C.

-- System Information:
Debian Release: trixie/sid
  APT prefers unstable-debug
  APT policy: (500, 'unstable-debug'), (500, 'stable-updates'), (500, 'stable-security'), (500, 'unstable'), (500, 'testing'), (500, 'stable'), (1, 'experimental')
merged-usr: no
Architecture: amd64 (x86_64)
Foreign Architectures: i386

Kernel: Linux 6.5.0-1-amd64 (SMP w/12 CPU threads; PREEMPT)
Kernel taint flags: TAINT_PROPRIETARY_MODULE, TAINT_OOT_MODULE, TAINT_UNSIGNED_MODULE
Locale: LANG=POSIX, LC_CTYPE=C.UTF-8 (charmap=UTF-8), LANGUAGE not set
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)
LSM: AppArmor: enabled

Versions of packages openssh-client depends on:
ii  adduser           3.137
ii  libc6             2.37-10
ii  libedit2          3.1-20230828-1
ii  libfido2-1        1.13.0-1+b1
ii  libgssapi-krb5-2  1.20.1-4
ii  libselinux1       3.5-1
ii  libssl3           3.0.11-1
ii  passwd            1:4.13+dfsg1-1+b1
ii  zlib1g            1:1.2.13.dfsg-3

Versions of packages openssh-client recommends:
ii  xauth  1:1.1.2-1

Versions of packages openssh-client suggests:
pn  keychain      <none>
pn  libpam-ssh    <none>
pn  monkeysphere  <none>
pn  ssh-askpass   <none>

-- no debconf information