Looking around line 714 you'll see..

$result = db_execute_assoc($srquery) or safe_die ("Error loading results<br />$query<br />".$connect->ErrorMsg()); //Checked
while ($srrow = $result->FetchRow() )
{
$_SESSION['srid'] = $srrow['id'];
}

My assumption is that since there should be only one row in the survey_(id) table for a given token, this while loop really only ever executes once. Which means either a) it will only execute once, in which case the while should be gone and potentially an error check should be added to assert that there is only one row in the result set or b) it can execute more than once, in which case the bug is that $_SESSION['srid'] will just have whatever the last value of srrow['id'] after having been over set however many times the loop executes.

Unless it really is the case that the query is allowed to return multiple rows AND that the value for the last row is the only one we want for $_SESSION['srid'] - in which case there must be a more straight forward way to make this happen than looping through all the rows, setting the value over and over until we hit the end.