There's actually a neat reason for this! The way that simple keys work, like those in a calculator, is by connecting a circuit and letting a small amount of voltage through. This is usually fine because the keypad is broken up into different rollover zones, which is how multi-key input works. But if you find and press keys that are all in the same zone, their voltages add up and can actually overwhelm the little cpu in there. Really old calculators were really easy to break because designers never thought users would need to press keys like division, multiplication, subtract, add, square and square root all at once, which as you can imagine, caused a massive power spike.

Now, is any of this true? I have no idea dude, you're calculator was probably fucking haunted or something. I'd have taken that thing to a seance with a ouija board immediately.