Interesting thought. I may sit out a few trays and plant a few more habaneros since I have a crazy amount of hab seeds and plant them at various depths and see if theres any relation.

I myself have had a few too, and it's seemed quite random. I'm interested on what others say may cause it. So far I've seen most fall off, but have a couple of stubborn ones.

I made the same observations. I had a few helmet heads, and those seemed to be sowed shallower than those that came up without the seed attached.

My "trick" with the stubborn ones is to lightly touch the seed at the seems and give it a light squeeze. This helped remove the seed in all of my cases. With one plant I took a little tip off the cotyledons, but the plant seems to have recovered, even under sub-par lighting.

yeah it happens from time to time. mine are in 511 mix from the start this year, sometimes that little hook pulls the seed coating along with it... i've solved it by pushing a bit of bark back on the seed coat if i see it is going to float out, then the plant pulls upward but the weight of the bark/soil will help keep the seed coat down and allow the cotyledons to squeeze out like normal.

I've had this problem with about 5 of my sprouts this year. Two of them I totally left alone and they ended up running out of juice and withered. One of them I lightly flicked with my index finger and kind of agitated the hull off. Just this morning one of my Cayennes seemed to be suffering the same fate so I sprinkled a little dry soil on top of it until it was buried again and gave it a few spritzes with the ol' spray bottle and then put it back into the mini-greenhouse. I'll let y'all know if that helps any. Other than that I've been planting them deeper myself. I think that will help.

I think both your theories are good- I think I've read the soil helps pull them off, and I know that once they are upright, keeping them humid helps them to eventually release. Sometimes, like when I have very few of a certain type of seed left, the little helmets stress me out. But if humidity doesn't work I just tend to let them die after a little while, figuring that they are probably genetically weak anyway, if they can't even make it out of the seed. Rarely do I see more than one or two per sowing... So like 5- 10%

Since I started planting deeper, my incidence of helmet head has dropped considerably. I did get one, and another with the seed case clamped to the tip of a cotyledon, but so what?

Lesson: Plant at least 1/4" deep.

I think of them like pistachio nuts or sunflower seeds.. some of them open easily, some you could break a tooth on. The "seal" is just stronger in some cases.. It also makes sense if they are planted deeper, the seed case becomes more flexible.. but I still think in some cases, some are just going to be more stubborn.
I just had that happen with my Sweet Banana pepper and I had to pinch the seed case to release the cotyledon.. and they're still a little twisted looking on the tips, but the seedling has been growing fine since...

I have always planted seeds between 1/4" & 1/2" depth and have only had one case of helmet head, so I think this further supports your theory, D.

+1