The following code should demonstrate that unusual behavior (becaue I'm still not convinced that this is a bug)

$input = array ( array (1,1), array (1,2), array(1,2), array(1,1) );
$result = array_unique ($input);
print_r($result);

The result is :
Array
(
    [0] => Array
        (
            [0] => 1
            [1] => 1
        )
)

This was not what I was expecting. I was expecting the following result :
Array
(
    [0] => Array
        (
            [0] => 1
            [1] => 1
        )

    [1] => Array
        (
            [0] => 1
            [1] => 2
        )

)

This is the result You get if You use PHP Version 4.0.4pl1 and before for example.
So it is up to You, if You call this a bug or if I just have missused the function array_unique because I was not using a one dimensional array.
Hopefully that helps You and me.

Cheers
Thomas