Pioneer system back-powering from a USB device

I just got a Pioneer system, and it seems to have a multitude of hardware and stability issues already.

The most annoying one right now, is that I installed a PiKVM (Geekworm PiKVM-A3). It connects from the RPi4a OTG port to a USB port on the Pioneer to emulate keyboard/mouse/cdrom for remote control.

When I have the USB cable connected and power off the Pioneer, it stays partially powered (the CPU fan runs slowly, but no LEDs are on). It also does not react to further power button presses from the PiKVM. Note that this is the opposite situation of the PiKVM being accidentally powered from the Pioneer, it’s the Pioneer drawing parasitic power from the PiKVM “device”.

It seems like there’s some protective circuits missing from the host USB controller schematics, that allows the host system to be reverse powered from a USB device. Has anyone else seen this? It seems concerning to me.

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