J. P. Gilliver (John) wrote:
I just had the loss of ")" again, so turned on NirSoft's KeyBoardStateView.

It showed exactly the same keypresses for "(" (shift-9) as for ")"
(shift-0), other than of course one had the 9 key and one the 0 key. But
I did notice that all the time it showed left Ctrl as pressed. Weird
thing is that actually tapping left ctrl had an effect (for example: I
have the Windows built-in utility on that draws circles round the mouse
cursor to help you find it if you tap either ctrl key, and tapping the
left [or right] ctrl key still makes the rings appear), so it doesn't
seem that the key is _actually_ stuck.

Tapping the left ctrl key a few times eventually made its "pressedness"
disappear from KeyBoardStateView - and hey presto, I could then type ")"
again!

It's still a puzzle: even if there _is_ a problem with the left ctrl
key, why should it stop me typing ")" - but leave me able to type "(",
"*", or any capital letter? [To recap: when this does cut in, I can
still type a zero, just shift-zero has no effect.] But at least I _may_
have a way of getting round it (other than cutting and pasting ")"s!).

This sounds like an Accessibility Feature.

One that "stretches" actuation of modifier keys,
so a disabled person can be just as productive
as everyone else.

In other words, *some* operation you are inadvertently
typing, keeps the "control" "jammed" for a period of
time, or until enough key presses have occurred to
cancel it.

*******

Keyboards in the past, used to have "private" signals for
shift, control, alt. They weren't on the "scanner matrix".

But as I understand it, newer keyboards may have been
modified such that those keys have been put on the
main matrix. The disadvantage of that, is if there
is an "ohmic" problem with the scan matrix, then
funny phantom key presses can be a result. But your
modifier stays asserted for too long, for that to be
a nice match for such a behavior.

Just a guess,
Paul