single.php is called twice for every post view – that was my conclusion after some investigations. How I’ve got it?
Trying to build the list of recently viewed posts I added simple tracking code into my active “Twenty Eleven” theme single.php template file. After that I’was wondered as I’ve got two records in my log instead the only one after any post view. First valid record for just viewed post and second unexpected record for post, which is chronologically next to the viewed post.
Thus WordPress post content rendered at least twice every time visitor clicks on its permalink. It is obvious and unneeded overhead for my opinion. Why it is happened? How to stop this weird behaviour?

Long period of waiting for the new WordPress 3.4 version was finished: if you were starving to get it, touch it, install it on your site, if you almost lost your patience, skipping all those beta 1, beta 2, Release Candidate 1, RC2 releases, if you even tried it at test environment, but still waited that great moment, when you could take it out of the box and put it to the live environment, if, finally, even some little part of written above is about you – we all together have very good news last week – WordPress 3.4 is here, with us! Download it, install it, use it, grow with it, and help to make it better :)!
What’s new in WordPress version 3.4?
– general speed enhancements. WordPress is faster and takes less processor time to fetch its data from the database;
– live theme preview. You can change theme appearance parameters and see how it would be on the fly;
– easy tweets embedding;
– HTML code in the images captions from Media Gallery is allowed now;
– and a lot of changes under the hood, not so easy visible as others, but very useful for developers.