A friend got me into the HP-71 nearly 35 years ago. He had one, and one time when I was with him, he pulled his out of his attache case and the memory was lost. I don't remember if it did an INIT: 3 or what. Apparently it had happened to him before, and he said he figured it was from keys getting pressed in the attache case. After I got mine and it happened to me a couple of times, remembering his theory, I had a woodworker friend make me a little box to put the soft case in, roomy enough for the case with all the QRGs and keyboard overlays as well. That was nearly 30 years ago and I have never had the problem since then. Here's a picture of it.