Yesterday I gave what I believe to be a valuable answer to a posted questions:
Get the dominant frequency of motion to correlate with tempo BPM of a song
This morning I find that the user has deleted the question. Had I not left it open a tab, I don't think I could have found it. My answer had an "undelete" option available, which when I hovered the mouse cursor over it, says "vote to undelete this post". When I click it, it informs me that an answer to a deleted question can not be undeleted. That makes sense, though I think the hover text should be fixed.
I searched for the topic here on the meta forum. I found a similar question to mine with the answer containing a reference to the deletion policy.
Had a second answer been added, or my answer upvoted, the user could not have deleted the question.
Now, I put a bit of effort into the answer, and I am fairly sure I solved the issue for the OP. I can speculate on why the user chose to delete the question rather than accept my answer, but it would be speculation. The obvious tactic to thwart this is to add a second answer to the question.
What the rationale is for allowing a delete once a question has been answered?
I did not read the Deletion Policy material closely enough.
From the Deletion Policy link:
"Deleting the question also deletes the answers. Deleting the answers undoes the hard work other people have put in to answer your question, and reverses the reputation they have earned too. This is not fair to the answerers of your question."
From Peter K.'s comment Help link:
"(the standard prevention against deleting answered questions is there so answerers don't lose rep, "
It seems that the policy values any loss to the reputation of the answerers more heavily than the effort to put into providing an answer. I think this is a poor decision as it provides a strong disincentive to put a large amount of effort into a first answer.
This has only happened to me this one time, but still, it has left me feeling a little gun shy. Should I wait until somebody else has posted an answer before I contribute mine? Should I add a followup as a second answer instead? Should I create a second account and upvote the first? None of these remedies seem appropriate or appealing.
I guess I've answered my own question to an extent. Thanks Peter K. and jojek.
If I should have put this as an answer instead of a followup, please let me know and I will change it.
Update: It happened again.