The person I purchased a rack from second hand had the flexiwatt burn a hole in the bottom tub. It's one with a recessed space for the tape too. So it was a bit odd for that to go.
Defects can happen in any product. I remember King of DIY had an issue with an underwater heater that boiled his stingrays years ago too.
I guess this is a good reminder to check a few of my flexi watt lengths later. I have one rack that does have the tubs on the tape. I try and check that one every 2-3 months for scuffs and damage. The others I usually just temp check from time to time. Maybe it's a good inspection time.