I didn't brew last weekend but I did spend some time in the garage dinking with the probes.
As you may recall, I had an issue with one of them seemingly getting stuck at 39.1 C during the last batch. I wanted to check whether it was the probe itself, or maybe something in the CAI WebControl board, so I took my 2000W heat stick and started to heat a few gallons of hot water from the tap. I moved the WebControl's probe to the Arduino and replaced it with a probe from the Arduino that I knew to be working.
When I dropped both probes into the bucket, it was already at 130 F or so. The probe attached to the Arduino immediately started indicating the correct temperature. (Well, after a couple of scan cycles anyway, as the stainless probe body heated up and transferred the temperature to the DS18B20.) The probe attached to the WebControl hit 130 F (54.4 C) and stopped changing.
Intrigued, I pulled the WebControl-attached probe out and cooled it. It started registering temperature drops almost immediately. When it read 99 F I put it back into the bucket, whereupon it decided to start tracking at the same rate as the other probe.
Speculation? The WebControl's firmware can't handle a too-rapid spiking of temperature, but when you let it ease into a change (i.e. it has a non-trivial ramp time) it does OK. Conclusion? None, except that the suspect probe from last weekend is good after all.