I recently asked a question, thought about it, decided to delete it, and I wanted to add a short note after deleting it explaining why I removed the question.
It turns out, I couldn't edit the deleted question. I searched for my other deleted questions (being a 10k user, I can do that), and it turns out that I cannot edit any of them. I can edit my deleted answers, though.
Moreover, this is unique to MathOverflow. On Math.SE it seems that I can edit my deleted questions just fine.