Q:

Why sometimes the selected answer is not the top answer?

I was under the impression the accepted answer gets always displayed before the other answer. However, I have noticed cases this does not happen, such as in this question:  How to get Google Desktop to index searchable pdf's.

A:

When sorting by votes, the accepted answer is promoted to the top, regardless of votes - unless it's a self-answer, in which case normal vote sort is used without promotion.
See also:
http://blog.stackoverflow.com/2009/01/accept-your-own-answers/

No change in sort order. Normally, accepted answers are “docked” under the question. This is not true for owner accepted answers; they stay in standard sort order like any other answer.

Accepted Answer not on top

Accepted self-answers aren't pinned to the top.

Self answer accepts should dock at the top, like any other post

