Neither Lipstick or Bull's Horn are hybrids so we can rule that out. They will cross with other C. annuums like jalepenos. Chitlepins are the hottest in this species. Have no idea what happened But interspecies crosses are rare and usually require intervention.

Kinda like why happened to my peperoncini's which were supposed to be hot but are as mild as a sweet pepper. odd things are a foot with those peppers.

Here is a link that might be useful: TheItalian Garden

I've read before that if a sweet pepper is merely pollinated by a hot pepper, the sweet pepper could be hot!

I found this:
"Seed Saving: Peppers will cross-pollinate, so separate by at least 500' or plant in insect-proof cages covered with window screen. Select peppers that are ripe, fully colored, and show no signs of disease to save for seed." *

Apparently my sweet pepper(s) were cross pollinated with hot ones. I still don't understand how the first peppers from this plant weren't hot, but today's was.

Also, cross-pollination is flower-by-flower (thus via each individual pepper), right? So if I saved seeds from several peppers from last year's plant, some of the seed could be true, correct?

*http://www.seedsavers.org/Education/Seed-Saving-Instructions/#pepper

Yes, your sweet peppers picked up hot genes from your jalapenos last year. Since you don't like hot peppers, I would ditch the seeds.

I have had peppers in which only the ribs and membrane were hot, and the cheeks were not. Maybe that's what you have there.

"I thought being "heirloom" meant it wouldn't cross with other plants."

Heirlooms are open pollinated. They will come true from seed as long as you prevent them from cross pollinating.

Pepper flowers are self pollinating and do not need insects. The flowers just have to be wiggled/jiggled/vibrated/moved around in some way (such as getting blown around in the wind) for them to set fruit. Insects do pollinate the flowers but they are not needed and are not wanted when you plan on saving seed. That's why isolation cages are recommended to prevent insects from cross pollinating. Bagging individual blooms will also work.

It's possible that some of your saved seeds will come true. But are you willing to go through the process of starting the seeds, tending the seedlings, transplanting, waiting for the plants to set fruit, and all this just to bite into a pepper that sets your mouth on fire? If it were me I'd start with fresh seed.

As for why the first ones you picked weren't hot, I oftentimes have hot peppers that are sweet or mild early in the season (such as my serranos this year). Especially if I pick them while still small. I attribute it to the cooler weather and the plants being young. But they soon correct themselves.

Rodney

Thanks for the replies. And Rodney, I appreciate the tutorial on pollination, it's exactly what I needed to know. What an interesting experience, but yes, you're right...a lot of time and effort put into a pepper plant which I can't use so out with those seeds. I wish these were tasty peppers; they're not, but they sure are pretty. Lesson learned!