I just noticed that several of the words I am just seeing for the first time appear as if I have given them a thumbs down. Meaning that the thumbs down icon is already highlighted a darker gray than usual. It's not on all newly seen words, but once I noticed it, I've seen it on 4 or 5 new words today. I don't know if you can see which ones I gave a thumbs up on today, but a couple of the ones I did were simply to remove what I thought was an accidental thumbs down that I hadn't intended to give. Some of my thumbs up were genuine thumbs up, though, so you may not be able to tell which were "buggy thumbs" and which were intentional.