Nikon USA has issued a service advisory for the reflection/flare issue on the Nikon D750 camera. You can check you D750 serial number on this website (here is the EU link) if is affected and needs to be repaired. And if your camera already got repaired, you will see a black dot inside the tripod socket on the bottom of the camera.
According to a leaked press release from Nikon USA, Nikon will announce a new firmware updates program called “I AM Advancing” on January 19th, 2015. This “I AM Advancing” firmware update program will allow you download new firmwares for Nikon DSLRs for free for first three years. On January 19th, there will be firmware updates for 6 FX cameras (D750, D810, D800, D800E, D610, D600). The new website for “I AM Advancing” will be located at http://imaging.nikon.com/advancing (not yet active).