I replaced my original Turbo and the new one did the same thing, the BACK, HOME and RECENT capacitive buttons stopped working occasionally. I realized the with the slick metal back on the phone, I was gripping it harder to make sure I didn't drop it. As a result, the lower right corner of the phone was pressed into the base of my thumb. (I am right handed.) My skin was folded over the edge and it was touching the screen. Once that happens, the capacitive effect is lost and the buttons don't work. I am getting a non-slip "case" to reduce the chances this will happen.
My fiance and I just hot the turbos about 2 weeks ago and she has been saying hers is doing the same thing I'll make sure to mention this to her and see if it helps. Thanks for posting this I was about to send hers in