time machine backup not using USB 3.0 speed

So, I have a MacBook Pro 17" early-2011. I have an expresscard 34 that has the FrescoLogic chipset (so it works natively with the board and with OS X, without any additional drivers). Normally, the USB 3.0 speeds work PERFECTLY with this card and allow me to use nearly the full potential of a given USB 3.0 drive. The only problem is when I use Time Machine to do my backups. The same drive that works super fast with any other app (even Finder) works super slowly when writing the backup. It can take 10 minutes to copy just 1.2GB. Why is this? Is the programming of Time Machine just that bad? When I restore from Time Machine (it's happened a couple of times) it works at the USB 3.0 speed. So confused