Fabia USB Port - low powered / quirky?

Ok, so wired in the other half's dash cam today... well nearly... got lazy half way through it and wired it to her USB port (arguing that I'd buy her an SD card to play her music off so we can ditch the USB Memory Stick)

Anyways, it doesn't kick off the dash cam recording when the engine starts as it should (and does when connected to power via. the cigarette lighter)

Any ideas why?

(for reference -> the dash cam is the Mobius Action Cam)