Description:
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I use rand(min, max) in a php script in a web page that is working pretty well.
But I also use it when this page open another (small) window
with another page that call the function rand() too.

This is working pretty well except when I reload the parent window and open again the small one, then the rand() function will return exactly the latest number !!!
Idem with srand() mt_rand()

For exemple on my parent window I click on my button "new"
this will open the small window and generate 5
I click again on "new" this will close and then reopen the small window and generate 8
etc . . . 
and then if I click on new and it'll open the small window
and generate for exemple 6
after that I reload the parent window and click again on "new" I will get a 6 again
After that if I click again on "new" it 'll be another one but if I reload the parent again, I'll definitely get a 6 again, and so on . . .

Reproduce code:
---------------
$nb = mysql_num_rows($resultMorceau);
if ($nob > 0)
{
	srand();
	$hasard = mt_rand(0 , $nb-1);
        echo hasard;
}

Expected result:
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I'd like to get a random number even if I reload my parent window frame !