I was able to reproduce this bug now, but only once, and only with libreoffice-gtk package installed. Before I had installed libreoffice-gtk, then Writer used Onboard quite normally, allowing me to type as much as I liked. After installing libreoffice-gtk package, then onboard hid after typing one single letter, but then after I re-summoned onboard, then it stayed up fine for more typing.
I was able to reproduce this bug now, but only once, and only with libreoffice-gtk package installed. Before I had installed libreoffice-gtk, then Writer used Onboard quite normally, allowing me to type as much as I liked. After installing libreoffice-gtk package, then onboard hid after typing one single letter, but then after I re-summoned onboard, then it stayed up fine for more typing.