XC60 brake problems

I'd like your advice on an issue with my 2010 Volvo XC60's brakes. I replaced the tyres at 62,000km and was advised that the disc pads and rotors would need to be replaced within about 5000km. I took it in at 65,000km to have the work done but it turns out that only the rear brakes needed doing. The mechanic tells me the fronts still have 100 per cent of the Volvo-specification thicknesses on both pads and rotors. So clearly, the rear ones have been doing all of the braking. He couldn't explain this and had never seen it before and I am wondering if you have come across a similar case before. Could something be faulty? Also, is it possible to adjust to even the wear, plus presumably make the car safer?