The peppers shouldn't be producing milder peppers from cross pollination right now. If you were to plant the seeds from those peppers then those seeds would produce milder peppers, but the fruit you are getting now is the fruit of the mother plant. Capsicum level in peppers is a self defense. Hot peppers are higher in capsicum and sweet peppers are lower. If you stress a pepper plant-- any pepper plant, the plant will respond by producing fruit with more capsicum. Is it possible that your plants were under more stress earlier in the season? From transplanting perhaps, or less water, hotter weather, etc? Do you have a lot of leaves on the plants now from lots of nitrogen in the soil? Plenty of water, rich soil, nice warm weather make pepper plants very happy, happy enough to not need lots of capsicum for self defense. DH is a hot pepper fiend. In order to keep his peppers really hot all summer long he starts limitting their water once the blossoms are set. Not enough to kill them, just enough to make them work a little. He also prunes them a little so they need to work harder to get food. Again the point is to cause a little stess. He also sprinkles a little coffee grounds around them. This raises the acid level just a little, again just enough to make them work. We've conducted experiments with plants side by side to see what effects these "treatments" achieve and there is definately a notable difference in the spiciness of the plants that are a little bit stressed. Hope this helps!