i would assume, the device is checking the power source and goes for read only on insufficient power supply - as USB 3.0 has more compared to USB 2.0
in general all devices should be backwards compatible to USB 2.0 or even 1.1 - and shall not show something like that - so i would further assume, you are having a noname brand item with most likely suspicies quality - but of course i could be wrong - just tell us what you have there