I've discovered that an obscure interaction between plymouth graphical boot splash and X, when plymouth falls back to text mode, is the cause of this strange behaviour.
A temporary workaround is to disable plymouth-splash:
sudo mv /etc/init/plymouth-splash.conf /etc/init/plymouth-splash.conf.disabled
I've discovered that an obscure interaction between plymouth graphical boot splash and X, when plymouth falls back to text mode, is the cause of this strange behaviour.
A temporary workaround is to disable plymouth-splash:
sudo mv /etc/init/ plymouth- splash. conf /etc/init/ plymouth- splash. conf.disabled