I have no idea how, but apparently 'slow keys' had got turned on at the login screen. Once I turned it off, it worked ok. I never normally use that.
OK, apparently like in bug 41427, if you hold Shift for long enough (like say by resting something on the keyboard), Slow Keys gets turned on, and it persists across reboots. And there is no warning that it's turned on. I can see how this would be useful for accessibility but there really should be a clue to people who get it accidentally set.
I have no idea how, but apparently 'slow keys' had got turned on at the login screen. Once I turned it off, it worked ok. I never normally use that.
OK, apparently like in bug 41427, if you hold Shift for long enough (like say by resting something on the keyboard), Slow Keys gets turned on, and it persists across reboots. And there is no warning that it's turned on. I can see how this would be useful for accessibility but there really should be a clue to people who get it accidentally set.