Hi there,
Yes, I believe it was I who found and fixed that a few weeks ago :-) You might need to upgrade to the nightly build, or if you prefer not to, I can post the specific 2 small code changes you'd need to make.
To patch your existing install, the file /zp-core/template-functions.php will contain two lines that read:
$rand_row = rand(1, $result['row_count']);
Change them both to read:
$rand_row = rand(0, $result['row_count']-1);
That should do it!