Steve,
You are a humdinger. I used to get a kick out of programming those calculators, too. They were a lot of fun.
I finally had to abandon the Algebraic Operating System found in the Texas Instrument brand, and begin using Reverse Polish Notation (RPN). I use that exclusively now.
You probably recall that it is never necessary to hit the Equals key. You enter the first number, then press <enter>, the next number, operation, number, operation, etc.
Of course, the HP brand did have superior physical qualities over my TI calculator, so that encouraged me to switch.
Bill