Are you quite sure of this? If one cylinder was not firing and the other five were firing, the engine would be down on power but would be somewhat smooth. This is provided that all of the other five are firing properly and the last one is not firing at all.

I'm more inclined to believe that one or more than one will not fire properly and you feel a miss in the engine for the first 15 seconds or so. If you let it idle, with no additional fuel, it will miss randomly with some kicking and banging which smooths out with time.

I have had the situation where it can continue to randomly kick for nearly 45 seconds after lighting off, if I give the plugs a very short cycle (10 seconds).

It appears that the longer that you run the plugs, the less likely the irregular firing will occur, and, if it does occur, the faster it will clean up.