Obviously nothing can be done about the behavior. Don't hate the players; hate the game.
You could remove the ability to propose your own post as the answer, much like you can't mark your own answer as helpful. That would probably be the best thing that could be done.
It would seem that each person likely thinks that their own post is the answer. The actual useful mechanism would be to retract an answer when you observe that someone else's answer is more appropriate than your own. I usually reserve the "propose
as answer" for those scenarios.
I'm not 100% sure, but would seem that you
do not get rewarded with points for marking a proposed answer, nor are there extra bonuses for having your answer be proposed or even for ultimately having a proposed answer marked as the actual answer. You do get a little congratulatory comment
that you "helped identify" a correct answer but I don't think it's worth any extra points. So we're already not rewarding people for doing it. [Please correct me if I'm wrong about this point system.]
If I am wrong, then removing the point rewards would be one step. Evaluating the utility of "propose as answer" is another good idea. I don't personally think much of it except when I feel like voicing a "me too"
kind of answer. If someone writes an answer which is exactly what I would have written (and this does happen quite a bit, especially with short code answers) then I will "propose as answer". Mostly to reinforce the fact that someone else
thinks that this is the answer without actually writing a duplicate post.
I also feel that it's wrong that the asker (or even a moderator) can un-propose as answer. That seems really wrong. You can't change my opinion. It's my proposal! The whole mechanism is really weird and I don't find it useful.
The actual usefulness would be a voting system where I could "agree" with a proposal. Somebody thinks an answer is right -- so what? It's better if I can say that I agree or disagree and collect the opinions of the whole community.
If an answer is already proposed, I can't further express my support for it. That's bogus too.
The up/down voting is OK, but I actually find it a little confrontational (I'm speaking from experience at StackOverflow). But it's more useful information statistically.
