I hope not, it's pretty new. I noticed that it does read a little bit higher than the actual temp of the beer though. I'm just thinking that maybe 8 hours isn't enough time to bring 4 gallons down to 50 from 65 in, say, a 45F fridge. My tap water is 47F right now so maybe I should take advantage of that while I can. I know DavidZach was saying something about infection from leaving it overnight.
Underpitching or under aeration doesn't seem a likely culprit, since this last batch, I stepped up a starter from 1L to 2L, then aerated for 2 minutes with pure O2. It's either infection or pitching too warm, I reckon. Unless anyone has anything other ideas.
I do have a new co2 system now, except the tank, so I think I can rule that out from here on out if this should happen again.