<?php
var_dump(
  array_map(
    NULL,
    array(1,2,3),
    array(4,5,6),
    array(7,8,9)
  )
);
?>

result:

array(3) {
  [0]=>
  array(3) {
    [0]=>
    &UNKNOWN:0
    [1]=>
    &UNKNOWN:0
    [2]=>
    &UNKNOWN:0
  }
  [1]=>
  array(3) {
    [0]=>
    &UNKNOWN:0
    [1]=>
    &UNKNOWN:0
    [2]=>
    &UNKNOWN:0
  }
  [2]=>
  array(3) {
    [0]=>
    &UNKNOWN:0
    [1]=>
    &UNKNOWN:0
    [2]=>
    &UNKNOWN:0
  }
}

while it should be

array(3) {
  [0]=>
  array(3) {
    [0]=>
    int(1)
    [1]=>
    int(4)
    [2]=>
    int(7)
  }
  [1]=>
  array(3) {
    [0]=>
    int(2)
    [1]=>
    int(5)
    [2]=>
    int(8)
  }
  [2]=>
  array(3) {
    [0]=>
    int(3)
    [1]=>
    int(6)
    [2]=>
    int(9)
  }
}