Question about occasional thin shelled egg.

I've gone back through some of the archived questions about this subject. Not too many because I'm lazy today. I have posted here before about why my hens sometimes lay thin shelled eggs and lack of calcium or illness or defective shell gland has been the usual suggestion. Well, I got another thin shelled egg yesterday. I used it this morning and noticed as the shell was lying beside another I used, that the interior of the shells are different. The normal egg is white inside from the membrane. The thin shelled egg seems to be lacking any membrane at all. If it's there, its extremely thin. Is this even possible? If so, what causes this? Does any one know?

Oh, and as a side note (completely different subject) back in November when we were on vacation for a week, one of our chickens disappeared. Our friend (upon my DH's instructions) let the hens out every day and made sure to lock them in the coop at night. On Wednesday night she noticed one missing. When we got back, we looked for her but couldn't find her. Not even a carcass. We figured that an animal got her and took her off. Well, Monday my son and I were coming home from the park and passed the neighbors house and noticed that their chickens were out and near the road. This neighbor is only 2 houses down from us and they have a rooster that we can hear. We noticed what appeared to be the same kind of chicken,a Buckeye, that we had go missing with two other breed hens. I'm wondering now if maybe this hen wandered over to their house. How do you handle something like that?
We had to mail order our Buckeyes from a Heritage breeder. They would only ship min. of 5 chicks of each breed. I don't think that our local TSC sells that breed, but I'm not certain.