php javascript causing blink on clicking any link in site

I am using a random quotes script on my site which shows random quotes on every click on any site link. Example: random quote 1 on index, if i click login, it shows random quote 2, 3 or 4 and so on. But the problem is that, If this script is on, Whenever i click on any other page of site, such as login, register etc. page does not load normally but instead it loads with a blink.

Here is the script i am using, with the filename quotes.php in my site.

<?php
$quotes = 'Random Text 01
Random Text 02
Random Text 03
Random Text 04
Random Text 05
Random Text 06';
$split_array = explode("\n", $quotes);
$rand_keys = array_rand($split_array, 1);

header("content-type: application/x-javascript");
echo "<!--\n
document.write('{$split_array[$rand_keys]}');\n
//-->";

?>
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And it shows up on overall_header.html These are the edits which i made in html file

<ul >
<!-- IF not S_IS_BOT and S_USER_LOGGED_IN -->
<li><script type="text/javascript" src="quotes.php"></script></li><!-- ELSE --><li >Important Information from the Administrators --</li><li >Thank you for visiting our forum. Please login to enjoy the full features of our site.</li><!-- ENDIF -->
</ul>
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Please tell me what bug in this script is causing blink on every page load.

Regards