x11-ssh-askpass (invoked via ssh-add) sets a size of 0x0 in WM_SIZE_HINTS. window managers using these hints are unable to properly size the window, so it ends up looking - in my case, using i3 - way too small. see https://tronche.com/gui/x/xlib/ICC/client-to-window-manager/wm-normal-hints.html originally reported at http://infra.in.zekjur.net/archives/i3-discuss/2015-November/002238.html thanks for a great toolkit!
direct link to the most relevant email in that thread: http://infra.in.zekjur.net/archives/i3-discuss/2015-November/002245.html
x11-ssh-askpass isn't maintained by the OpenSSH team. It used to be maintained by Jim Knoble at http://www.jmknoble.net/software/x11-ssh-askpass/ but that domain seems to be gone now.
The last copy of that site on archive.org (https://web.archive.org/web/20131006102910/http://jmknoble.net/software/x11-ssh-askpass/) says "The OpenBSD folks are maintaining their own port of x11-ssh-askpass. It's available in the X11 section of OpenBSD's anonymous CVS tree." Which indeed seems to be true (http://cvsweb.openbsd.org/cgi-bin/cvsweb/xenocara/app/ssh-askpass/) although by the "last touched it" rule, the maintainer is jsg@ rather than the openssh team. There's also a mirror on github although it looks like there's never been any work done there. https://github.com/sigmavirus24/x11-ssh-askpass
thanks for your help Damien and Darren. on further inspection, it seems the arch linux package pulls x11-ssh-askpass from http://pkgs.fedoraproject.org (see https://projects.archlinux.org/svntogit/packages.git/tree/trunk/PKGBUILD?h=packages/x11-ssh-askpass) so perhaps i should direct my bug report there.
Close all resolved bugs after release of OpenSSH 7.7.