Answering one's own question is A Good Thing, but what about when there is no value in the question or answer?
An example is Android TextView.setText() is appending, not setting. where there is an underlying issue that isn't addressed in the original question, the OP solves the underlying issue, and answers the question with a general "turns out I xxx and there's no problem thanks for your time".
What if anything should be done about this? Personally, when I've asked a question that turns out to have an underlying cause, I've edited the question to explain what was going on and provided the resolution.