It is not obvious that only the front ports have problems. Some people have problems with front ports, some with the rear ports. It depends also on the OS, Windows 7 32 bit and 64 bit drivers behave very differently for Etron.
With driver 0.105 I have problems with the rear ports not recognizing anything connected and the front ports working almost properly.
I think mainly the problems are driver related, but when I have tested my external HDD with Crystalmark, I have touched the EJ168A chip and it was very hot.
The rear USB 3.0 ports are directly connected to the P67 or Z68 chipset. The front USB 3.0 ports are connected through a PLX chip and they will be slower because of this.
The best drivers are the 0.101, they work properly with specific USB devices. If you have only those compatible devices, you will likely have less problems.
The drivers have been screwed up in version 0.104 when JMicron support has been added. My guess is that the external HDD enclosures with the JMicron chipset have needed very different timings, but changing the timings has affected all kind of devices which previously were working.
In my opinion Etron has no much experience writing USB drivers. In the past they had some webcams, but that experience is not enough for writing USB port drivers.
What is pissing me off, is that when a device is not recognized by the USB 3.0 port, this will cause a dead-lock in the drivers and at some point this will cause BSOD.
I think most of the problems can be resolved in the drivers. I don't know how to solve the overheating, maybe by reducing the performance and adding some heat-sinks.
I think I will add a PCI-E card with the NEC chip and disable the Etron controllers for a while. I expect maybe in a couple of months they will have better drivers.