Depending on the construction of the coil in the atomizer, it may be that liquid is continuing to vaporize a second or so after you release the button. Even at "only" 40 Watts, the coil doesn't just go cold after being lit with the same energy as a household light bulb.
If you mean that the
device continues to send energy to the coil after releasing the button (like you're still holding it), that's a problem with the switch. That could be caused by some gunk and/or debris around the button. A toothpick (or a bamboo skewer or a broom straw) might get that outta there.