RK3588 boards may leave their fans spinning at full speed when powered off

An oddity I've noticed and I've never had the time to look properly into: when powering off RK3588 boards, like to ROCK 5B or the ROCK 5T, the fan may start spinning at full speed. This happens regardless of whether the fan was visibly spinning at the time the shutdown command was issued.

I assume this is because the pin is put into a fixed power state, which will make the transistor that's controlling the fan voltage pin conduct. An alternate explanation is that the PWM output freezes at the current high/low state.