I was reading this question, and I had started writing my answer, but then once I posted it I noticed the question had been put on hold, and was wondering: Why can you still answer on hold questions? It seems rather counter intuitive (or at least ineffective) that such questions can still be answered, although I am glad my time wasn't wasted on that answer.
When a question is put on hold, the button to add a new answer is removed. However, if you've already clicked that button and started writing an answer, the process is allowed to conclude. This is similar to why an answer to a question on hold can be edited.
Update: Tim Post says that if WebSockets are operating properly, a periodic message is sent to the browser that should disable the "Submit" button. Sometimes, WebSockets fail (or are not supported by the browser), and the "Submit" button remains enabled, even after the question is closed.