So this topic has been discussed multiple times on Meta. I am posting this to report a specific incident. This homework question was deleted by its author shortly after an answer was posted. Yes, the author already had the answer and had just posted the question to confirm it, but I still don't see how that makes this kind of thankless behavior any less acceptable. I would have upvoted the answer to prevent this deletion(I usually do) but I didn't even get that window of time. I only realized because I had left a comment telling the author his answer was almost correct, he missed a factor of $3$. When trying to comment back that I had misread the original question due to lack of $\rm \TeX$ and his answer was infact right, I got the usual message saying that comments are disabled on deleted posts.
So is this acceptable, just because the author already had the solution? If it isn't how is this kind of situation usually handled?
Also what should I do when I notice this? An entire meta post for a single incident seems like overkill, but I don't have 10k+ rep so I can't even view the post anymore let alone flag for mod attention, (if that is possible on deleted posts).