I haven't noticed but I will try to remember to pay attention next time I change out the coil. When I replace my coil I do a burn-in after I put it in. I don't let it go totally red, I pulse the fire button on my Coil Master 521 Tab. After I will put the Koh Gen Do in the coil and assemble the topper and check for a short and note the ohms.
Do you do a burn-in of your coil?