P2715Q, USB stays ON in suspend mode?

I've ensured the menu says 'USB - off during standby', but the USB is powered even when it's said 'entering power save mode' and then blanked the screen with the power light flashing to indicate standby. The only thing plugged into the monitor's USB is a desk fan, and I don't want it on while I'm not there. This used to work with my Mac, but not with this PC. Is it because I'm using HDMI instead of mDP?