The ZTE V987 is also known for an not so good thing: The "return button problem", or in other words, too sensitive to touch, so that would make the "back" button activate without directly touching it. Quite annoying.
My phone had that problem on earlier software, but the good news is that after I have upgraded to a 3.20 based ROM, the problem is gone! So it seems that it was a software problem after all.
I need to say, that my phone is from the 2013.03 production or "second lot".