A7N8X DL and SD/MMC on USB3

Hi,

I have an MP3 player (with 256Mb onboard and 256Mb SD/MMC) that I
connect to my A7N8X DL. That works fine as long as I use one of the
four USB ports thats is already mounted on the motherboard.
When I try to use 'USB3', which is connected to the front USB
connectors of my Aopen case, it does not work that well anymore.
Sometimes it looks ok (but I then get I/) errors), other times the 2
mass storage drives are not even recognised.

I then added an 6 in 1 card reader to my system. It also included USB,
firewire and audio. I connected the USB cables of this reader to the
same USB3 connector on the motherboard. When I now connect the MP3
player to the USB port, the results are similar.
I removed the MMC/SD card from my MP3 player and inserted it in the
6in1 reader. Similar results! Impossible to copy files to or from the
SD/MMC card.

Is USB3 different from the other two USB hubs on this motherboard? And
how to explain this strange behaviour?

Edgar