When writing a .odt document on Libreoffice Writer in Ubuntu 12.04 with Gnome 3 (using Gnome Shell, not Unity), if word autocompletion occurs too fast, the whole Gnome 3 environment freezes, with keyboard not respondig (LEDs don't change state when pressing those keys) leaving as only alternative to force shutdown of the laptop computer using power button and restart the entire operating system, possibly loosing lattest changes in document and risking to filesystem corruption.
My graphic card is an Intel HD integrated card and mi processor Intel Core i7.
I have no problem with this on Ubuntu 12.04 gnome shell with LibO 3.5.4.
Perhaps some kind of driver bug.
You could try reporting it to Ubuntu directly on Launchpad.
I also have no problems with Ubuntu 12.04 and gnome-shell 3.4.1 and LibO 3.6.0
Not positive what the issue is but you might at least start here: