Windows 7 - Strange issue with Usb ports on boot

Hi everyone, I've built a new pc based on the X79 chipset. Everything works great, I'll probably post some benchmarks elsewhere in the forum.

There's only one strange problem: sometimes usb devices won't get recognized on boot. The mobo has a lot of usb ports, both 2.0 and 3.0. The glitch has happened with two usb devices in particular, usb port version notwithstanding.

The devices are a scanner and the communication cable between the pc and my ups.

When the glitch happens, I have to go to control panel, disable and re-enable the device and it will usually get recognized. Sometimes this doesn't work and I need to detach and re-attach the usb cable to fix the problem.

Does anybody have any idea what may cause this behavior?

Thanks in advance for your help.