I figure I may as well post this although I'm convinced this was somehow my doing. When held vertical, a dead zone on the capacitive touchscreen is located at the bottom center, right where the notification button is if you were to open the menu. When the call screen is active, the dead zone seems to inch up some, and now prevents the use of the end call button.
When the phone is horizontal, that spot becomes the center right - and works perfectly. the dead zone now goes from top to bottom across the entire screen, leaving only the sides usable.
Verizon called it "a definite defect" and are replacing it with a refurb, which I'm not particularly happy about considering the sales rep that talked me into the insurance said it meant a new phone. But that's another story.
Anyone else encounter this problem?