I may have experienced this as well. I had two out of five heads that either had hot legs or had this kind of short. The resistance before firing was normal .15+-.01 . Upon inspection, the nickel of one of the legs was blackened.
I agree with you however that the DNA40 chip itself works well. I absolutely love temperature control on every one of my attys with the sole exception of the subtank mini with prebuilt heads. If i use the rba section, which I do a lot, the vape is perfect. Must be the TSCs.
The more comments about the mini and pre-made coils make me wonder if there is something about the mini that is different than the nano....where the coil screws into the base... not having a mini I can't comment....