Free42 bug, or my mistake?

[jebem]

Do you mean the Thomas Okken "Free42 — An HP-42S Calculator Simulator"?
I never tried it, but it seems a nice project, it evens has binaries for Windows!

That said, I prefer to use emulators where the real ROM firmware from the original calculator is used. It will give a closer behavior to the real physical device.

There a few emulators for the HP-42S, I am using at the moment the Christoph Giesselink version for Windows.

In case You do not run Windows natively, you can use a hosted hypervisor for your preferred hosting operating system.

By the way, what is the 42S manual that you are referring to?
Maybe I can duplicate the issue in my emulator program here.