Hello. I have purchased an (3000) Apple iMac 27 3,5 GHz i7 with 16GB RAM and 4GB VRAM GeForce GTX 780M (S.N.: DGKLN017F8JC) in December 2013 and Im currently experiencing quite severe image retention problems. All white portions of the screen that remain still for 20 or more minutes remain as a blue shadow on grey(ish) colours. As soon as the problem started appearing I took it, under warranty, to the official Apple Repair store (early December 2014) and they exchanged the screen. After picking it up, the problem remained and I took it to the store again. They were two weeks trying to find the problem and I had to go to the store myself to replicate the effect which was then confirmed by the technicians by naked eye. I received a call a few days later telling me the problem was solved but, again, when I got to the office the screen was still experiencing the same problems. Now Apple tells me that this is expected behaviour and therefor recuses to service my mac! I even sent a registered letter to Apple Distribution International and received a rude reply saying that this is expected behaviour. I work everyday with image and the ghosting is easily seen and interferes with my work. Is it expected behaviour? Couldn't it be graphics card? I have owned several macs and this is the first time this happens and, frankly, I'm quite disappointed with Apple Service on a machine under warranty.