The a11y-settigs plugin turns toolkit-accessibility off when neither screen-keyboard nor screen-reader are known to be active. Unfortunately this seems to happen not only when the gsettings keys are actually toggled by the user, but under certain conditions also right after login. I can reproduce this here with Unity and GNOME Shell sessions.

Onboard needs a11y for auto-show and word-suggestions. Problems arise if Onboard is started by scripts, without having the screen-keyboard-enabled key set, as is necessary in advanced configurations like switching between laptop and tablet mode described in the original bug report here:

https://bugs.launchpad.net/ubuntu/+source/onboard/+bug/1227173

I'm wondering why a11y has to be disabled at all. Is this still a precaution due to stability or resource usage concerns? I'm biased of course, I'd prefer to keep it enabled at all times, irrespective of the screen-keyboard and screen-reader keys. However, it would already help a lot if g-s-d wouldn't turn it off right after login.

TEST CASE:
$ gsettings set org.gnome.desktop.a11y.applications screen-keyboard-enabled false
$ gsettings set org.gnome.desktop.a11y.applications screen-reader-enabled false
$ gsettings set org.gnome.desktop.interface toolkit-accessibility true
- log out and in again, perhaps hard reset or reboot with magic SysReq is necessary
$ gsettings get org.gnome.desktop.interface toolkit-accessibility
false

'gnome-settings-daemon --debug' after login says:
(gnome-settings-daemon_:2229): a11y-settings-plugin-DEBUG: screen reader or OSK enablement changed
(gnome-settings-daemon_:2229): a11y-settings-plugin-DEBUG: Disabling toolkit-accessibility, screen reader and OSK disabled

System:
Ubuntu 13.10
gnome-settings-daemon 3.8.5-0ubuntu4
gnome-shell 3.8.4-0ubuntu5