Has anyone ever had a piece of flexwatt go on the fritz? This seems so odd because I really thought they were foolproof...

I moved from college back to home recently, and I set my snakes up the way I usually do - Ranco probe on Caspie's flexwatt, and Caspie and Luke's flexwatt pieces plugged into that same Ranco. Everything seemed to be working fine that night - temps were good, I checked everybody. But the next morning, I check the tubs, and the temp on Caspie's flexwatt (displayed on the Ranco) was in the 70's - yet the t-stat's power strip had been on for god knows how long, and Luke's flexwatt temp was through the roof around 105*F!! Thank god Luke was on the cool side - smart boy!!

Now I know it is not the Ranco and indeed Caspie's flexwatt, because after this happened, I let everything cool down, then switched the probe to Luke's flexwatt - this time his heated up normally to 92 and stayed there, but hers still was not heating up properly...

I ordered a new piece of flexwatt and it is en route, but what happened here!? Do you think it was something I did, or do they just periodically malfunction...? Could a power surge have caused this (although I don't remember one occurring, it's possible)?