If all you want is a single element from an array, try this. If you still get goofiness then there might be something wrong with your random seed. All that said, I still wonder if there's something going on with your browser and the server. Do you know how to try this right from the command line? I would, just to prove thatPHP is behaving correctly/incorrectly.
<?php
$input = array("Neo", "Morpheus", "Trinity", "Cypher", "Tank");
$key = rand(0, count($input) - 1);
echo $input[$key];
?>