Description:
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array_unique seems to be losing a value somehow when two 
arrays are merged that contain the same value. I am 
merging two arrays, then feeding the result to 
array_unique. (What I REALLY want is a set!) print_r 
seems to show a proper result. However, waling through 
the array results in an empty value. In this 
case, 'IsNew' is missing. I changed the order of the 
merge, and a DIFFERENT value was missing!

If merging the two arrays results in a set (no 
duplicates), then array_unique seems to work fine.

Reproduce code:
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// $InfoThumb AND $PopupThumb determine what fields to fetch. Build the proper query string.
$fieldNames = array_unique(array_merge($PopupThumb, $InfoThumb));
print_r($PopupThumb);
print_r($InfoThumb);
print_r($fieldNames);
for($i=0; $i<count($fieldNames); $i++)
	$fields .= ', ' . $fieldNames[$i];

$inc = $NumberOfColumns * $NumberOfRows;
$sql = "SELECT ID, ImageThumb, ToShow $fields FROM Gallery" . $sql_filter . $sql_sort;
if($total >= $inc) $sql .= " LIMIT $start, $inc";

die($sql);

Expected result:
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SELECT ID, ImageThumb, ToShow , 
Title, Price, IsNew, Medium, Width, Height, Depth FROM 
Gallery WHERE ToShow=1 ORDER BY Updated DESC LIMIT 0, 10

Actual result:
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Array (  [0] => Title  [1] => Price ) Array (  [0] => 
Title  [1] => Medium  [2] => Width  [3] => Height  [4] 
=> Depth  [5] => IsNew ) Array (  [0] => Title  [1] => 
Price  [3] => Medium  [4] => Width  [5] => Height  [6] 
=> Depth  [7] => IsNew ) SELECT ID, ImageThumb, ToShow , 
Title, Price, , Medium, Width, Height, Depth FROM 
Gallery WHERE ToShow=1 ORDER BY Updated DESC LIMIT 0, 10