Q:

re-accepted answer does not reward +15 again?

Looks like OP miss clicked on the tick - any reason why the +15 isn't reinstated?

A:

Because your answer became community wiki before accepting it again.
Exactly what happen:

Your answer was accepted on 2012-09-11 at that time it was not a community wiki answer so you got +15 for that.
Then your post became community wiki post on 2012-09-21.
Then OP unaccept it (may be by mistake) so you lost 15 reputation.
Then again OP accepted it. So you did not get 15 reputation as it is community wiki post.

A:

You have edited your answer more than 10 times ( which is 16 revisions ), hence your answer become Community Wiki answer automatically. 
As per the rule of the Community Wiki Answer, it doesn't generate any reputation, that's why you are not awarded +15 reputation again.

