Powered USB hub causes resume from standby

I have two powered USB hubs, one connected to a USB port on my PC, and the
other connected to the first hub. I have my PC and most of my peripherals
connected to an Intelliplug panel, which shuts off power to the connected
peripherals about 3 seconds after the PC is shutdown or put into standby.

I've just changed my PC system unit to a Dell Inspiron 530s running Windows
XP-SP2, and am finding that when the Intelliplug shuts off power to the
directly connected hub after the system is put into standby, the PC
immediately resumes from standby. This problem rather detracts from the
convenience of the Intelliplug. Rather strangely, by experimenting I've
found that if I leave the directly connected hub switched on, shutting off
power to the second hub does not cause the system to resume.

I did not have this problem with my previous PC system unit, also running
XP-SP2. The peripheral configuration was the same.

I've tried changing the settings on the USB port to which the hub is
connected, to stop XP shutting off power to the hub. This didn't make any
difference. I've tried disconnecting the hub from the Intelliplug, and
waiting longer before switching the hub off manually, in case some sort of
noise from the Intelliplug was causing the problem, or a longer wait would
help - again it made no difference.

I can't think of anything else to try. Dell's technical support said that
the PC is performing as specified, but I'm not yet convinced there's no
solution, given my previous PC did not suffer from the problem.

I'd welcome any ideas.

Ryder Cowan