<?
$haystack = "123456789";
$needle = "1";
$tmp = strpos($haystack,$needle);
if ($tmp)
{
	printf("Yes");
}
else
{
	printf("No");
}
?>

This prints no, because it returns 0 which is the same as false.

The documentation says:
If needle is not found, returns false. 

The problem if needle is at position 0 i haystack then it returns 0 which seems to be the same as false, therefore if needle is at position 0 
you get the same result as if it is not in haystack at all.

I don't know if this is a bug or just something that should be mentioned in the documentation.

Feel free to mail me.

Regards
    Martin.