I only use RPN & RPL calculators, so for me % is a binary operator. Using % as /100 seems acceptable, even maybe coherent, but I think it is also less useful and even strange to mean Joe (9 * 5 % to compute the 5% of 9, that's clumsy, my TI Datamath II did it in the 70s, we are now on the XXI century). In any case, not a matter to rise a case over, provided that different calculator manufacturers & programmers have not reached a consensus on this.
Hyper Calc performs calculations with the number P of digits you set (calls it precission, depends on portrait/landscape layout), and displays numbers with the number D of digits you set (must be D <= P). Five minutes using the app and one gets this. So, IMHO, this OP's rant was user error.