HP 12C ATSAM4L version: ON-f-ENTER

[brouhaha]

I was trying to remember the key sequence to get the firmware version of ARM-based HP 12C calculators (which starts with ON-g-ENTER), and before I hit upon the right combination, I tried ON-f-ENTER. After doing that, the 12C behaved normally, except that it would not turn off. The ON key after that was completely ignored, until I reset the calculator.

Has anyone else noticed this? I've only tried this on a recent ATSAM4LC2C based 12C, not the earlier ATSAM7L128 version. It seems to be reproducible. I imagine it's intended as some kind of factory or R&D test mode.

Some might find it amusing that I discovered this by accident when poking keys with my fingers, and not by spelunking through the firmware.