Why are these mushroom stems leaving a long, skinny fiber behind on the cap? I was pulling the stems out of some mushroom caps today - we save the stems and make broth out of them - when I discovered that some stems weren't coming out all the way. Have a look: 



Mushroom fanatics out there: Any idea what causes this? Is there something wrong with these mushrooms? Am I being paranoid because I just read this question?
Mushrooms are complicated little guys. What you see as a single type of mushrooms is actually hundreds of different substrains. Its possible they're from a slightly different batch than what you're used to, and so have slightly different stems. I wouldn't worry about it, and enjoy the mushrooms!