Exactly the same happens on my old TP 570, too. No way to turn it off.
Here's an explanation of this phenomenon:
<< Electrically, keyboards are grids of crossed address wires, which
can be connected together arbitrarily at their crossover points when
you press keys. Every time you press a key, you connect wires
together; the keyboard hardware looks at which wires are connected to
tell which keys are being pressed.
If more than one connection's being made on a given wire, though, the
keyboard hardware won't be able to figure out which keys you're
pressing. If a theoretical keyboard had one horizontal address wire
for each row of keys, then you wouldn't be able to press any two keys
on the QWERTY row simultaneously and have anything happen.
I don't know whether any real keyboards are this simple. I suppose
some real cheapies may be. Better keyboards split up the 'board into
separately addressed zones, which may or may not all be composed of
contiguous blocks of physical keys. There are numerous designs out
there, and also differently intelligent hardware on the other end of
the matrix, which may or may not be able to handle more than a given
number of keys at once no matter where they are.
There's a specific "too many keys" error that keyboards can report,
with which the operating system can do what it wishes. I speak from
recent experience when I say that Windows generally system-beeps
repeatedly at you when it gets this "cat-on-the-keyboard" error. Some
keyboards have their own noisemakers and will beep or click at you
when the error occurs, no matter what OS you're running.
If I space my hands over my old IBM battleship carefully enough, I can
press a key with each finger and not get the too-many-keys beep. This
isn't of much interest, though; if I don't space the keys I'm pressing
out, I often can't press more than three at a time. Three nearby keys
at a time is enough for most *** purposes, though; press any three
of your WASD keys at once and one of them will be contradicting one of
the others anyway.
You can work out empirically which combinations of keys a particular
keyboard supports, by just fiddling around with a text editor window
open. For all of the keys except the modifiers (Control, Alt, Shift)
and other special keys, the last one you pressed ought to repeat if
the combination's OK, and nothing should happen (possibly with error
beeps) if you're pressing too many. It's easy enough to do this before
buying a keyboard, if the store staff will let you.
My IBM, for instance, lets me press ASD at the same time with no
problem, likewise SDF, or indeed ASDF together. But not DFG, FGH, GHJ
or HJK. But JKL is OK again, as is KL;. Not L;', though. Various
sub-combinations of non-allowed combinations are OK, though; D and F
and any letter on that row except G are fine. Et cetera. >>