Google Chrome: PHP code would be executed twice when session was started - php

Question

I need to set a dynamic id for every document load. This ID should be set in PHP. Now, when i set a session_start(), the php code would be executed twice because the ID-code in generated document source differs from the same code in the alerted script variable. There are no runtime errors.
What's wrong with this code and how can i prevent the session to re-execute my code after session_start() ?
And when the code would be executed twice (var idvar contains a different value) why the heck is alert executed only once?
I simplified the script so you can try for your self:
<?php
// Session start generates two different ID's
session_start();
// Create ID
$time = microtime(1);
$parts = explode('.', (string)$time);
$idvar = strtoupper(strrev(dechex($parts[0]) . dechex($parts[1]))) . dechex(rand());
?>
<script>
// Contains a new generated ID after session_start()
var IDvr = '<?php print $idvr; ?>';
alert(IDvr);
</script>
Screenshots:

Answer 1

Try move the id initialization just before session_start() i suspect it related on how things executed in php after session_start().
Edit
still unable to reproduce it

Answer 2

I found this:
PHP Session storing behavior into variables?
But even when i add a favicon to the page it don't works. Also the page is standalone and not included as require in another page.
Even this is not working!
// Session start generates two different ID's
if(!isset($_SESSION) && !isset($idvr)) {
session_start();
// Create ID
$time = microtime(1);
$parts = explode('.', (string)$time);
$idvr = strtoupper(strrev(dechex($parts[0]) . dechex($parts[1]))) . dechex(rand());
}
Update:
Now corrected:
With view-source:pgname and session initialized the code would be executed again in source view!