Well, took my phone that was doing this to Verizon tonight. Was able to demonstrate to the rep what the problem was, and also told her the steps I took to try and correct it (hard reset, pull battery, etc...). Also showed her the results from the Sensor Test App. She didn't even argue with me, just said she'd replace it. I was able to show her the issue by standing under one of the ceiling lights in the store. She did say this was the first time she'd seen this issue, but had seen one Droid where the screen didn't turn off when in a call and the phone was held to the ear, which resulted in several mistakenly ended calls. Once I got the new phone, I tested it with various lights in the store, and even held it directly under one, and it worked exactly as it should, so Yay!
Just in case anyone wonders, this one is marked 41/09, and my old one was 39/09 (I think, could have been 38/09).