So as I understand it, Sony claim that the wireless charging knackers the battery. Their solution is to sell you a very expensive http://www.amazon.co.uk/Sony-WCR14-Wireless-Charging-Xperia-Black/dp/B00NCR50CG/ case and dock.
Annoyingly the case with the "Smart Window" is different, and their is no Copper version of the charging case. http://www.amazon.co.uk/Sony-SCR24-Style-Cover-Xperia-Copper/dp/B00N9OC674
I ordered the cheaper case and after two months of delays and excuses I cancelled and ordered a third party one. Which actually was 20% of the price and is much, much nicer.