it may be because the usb port not only provides info but also powers the device so if the devices plugged need more supply than what the usb can provide they won't work.
I have experienced something similar with an external hard drive unit for my PC that can be powered with the usb or using an external power supply. on a PC the usb is more than enough for it to work but if I use it on a tablet I need to use the external power supply for it to work (and thank god for it)
