Because mine did. I don't even know where to report this as a bug, and I don't wanna remap all the Fn functions.
Thee were upgrades to systemd and gnome shell. The keys have switched places even on the gettys. I'm not sure if it's a kernel thing, or part of Debian's keyboard setup black magic. I've masked keyboard-setup, changed the configuration with dpkg, but no dice. It was working before the last set of updates and a reboot, so one of the packages must have changed something. The firmware doesn't have the option to switch the keys, so I'm pretty sure it's not that.
This is a hardware issue, not a Debian one. Good thing I didn't open a bug.