It should be mentioned that array_diff only checks one dimension of an n-dimensional array.

for example:

Array
(
   [0] => Array
               (
                [0] => "test"
                [1] => "lala"
               )
)

is the same like 

Array
(
   [0] => Array
               (
                [0] => "test"
                [1] => "bubu"
               )
)

when checking Array with array_diff.

Only when checking Array[0] with array_diff it returns that the arrays differ