He/she said it doesn't work when plugged into the front USB ports:You can use both front USB ports for your GameCube adapter with Rumble, and keep both back ports for your USB HDD Y cable.
I tried plugging the adapter using the front usb ports but they do not work just looking for a workaround here...
It's strange, though. I use the front USB ports for my adapter and it works fine with HID to VPAD. By the way, I use the bottom USB port on the back of the console for my HDD, and the left USB port on the front for the adapter's black plug.