It would seem that you've created a short between an unswitched 5V output of the power supply (the Vbus of the USB port) and a switched out (the 5V wire in the disk drive cable).

Yes, this is a Bad Thing. When the PC is switched off, the unswitched output of the power supply is now overloaded trying to drive all of the loads on the switched output.

The question you linked to is about driving a single USB charging port from a standalone ATX supply — one that isn't also being used to power a PC. What you are attempting to do (powering an entire hub from a shared supply) is definitely not recommended unless you know exactly what you're doing.

It would seem that you've created a short between an unswitched 5V output of the power supply (the Vbus of the USB port) and a switched output (the 5V wire in the disk drive cable).

Yes, this is a Bad Thing. When the PC is switched off, the unswitched output of the power supply is now overloaded trying to drive all of the loads on the switched output.

The question you linked to is about driving a single USB charging port from a standalone ATX supply — one that isn't also being used to power a PC. What you are attempting to do (powering an entire hub from a shared supply) is definitely not recommended unless you know exactly what you're doing.