Description:
------------
In an array, a sub-sub-key of an existing key is now returning a letter of the value indexed by the main key.  This is a regression in 5.4.  PHP 5.3 still operates as expected.  I suspect this is related to the array dereferencing changes.

Test script:
---------------
$arr = array('exists' => 'foo');

if (isset($arr['exists']['non_existent'])) {
    echo "expected: sub-key 'non_existent' is set: ";
    var_dump($arr['exists']['non_existent']);
} else {
    echo "BEHAVIOR CHANGED: sub-key 'non_existent' is not set.\n";
}
if (isset($arr['exists'][1])) {
    echo "expected: sub-key 1 is set: ";
    var_dump($arr['exists'][1]);
} else {
    echo "BEHAVIOR CHANGED: sub-key 1 is not set.\n";
}

echo "-------------------\n";
if (isset($arr['exists']['non_existent']['sub_sub'])) {
    echo "BEHAVIOR CHANGED: sub-key 'sub_sub' is set: ";
    var_dump($arr['exists']['non_existent']['sub_sub']);
} else {
    echo "good: sub-sub-key 'sub_sub' is not set.\n";
}
if (isset($arr['exists'][1][0])) {
    echo "BEHAVIOR CHANGED: sub-sub-key 0 is set: ";
    var_dump($arr['exists'][1][0]);
} else {
    echo "good: sub-sub-key 0 is not set.\n";
}

echo "-------------------\n";
if (empty($arr['exists']['non_existent'])) {
    echo "BEHAVIOR CHANGED: sub-key 'non_existent' is empty.\n";
} else {
    echo "expected: sub-key 'non_existent' is not empty: ";
    var_dump($arr['exists']['non_existent']);
}
if (empty($arr['exists'][1])) {
    echo "BEHAVIOR CHANGED: sub-key 1 is empty.\n";
} else {
    echo "expected: sub-key 1 is NOT empty: ";
    var_dump($arr['exists'][1]);
}

echo "-------------------\n";
if (empty($arr['exists']['non_existent']['sub_sub'])) {
    echo "good: sub-sub-key 'sub_sub' is empty.\n";
} else {
    echo "BEHAVIOR CHANGED: sub-sub-key 'sub_sub' is not empty: ";
    var_dump($arr['exists']['non_existent']['sub_sub']);
}
if (empty($arr['exists'][1][0])) {
    echo "good: sub-sub-key 0 is empty.\n";
} else {
    echo "BEHAVIOR CHANGED: sub-sub-key 0 is not empty: ";
    var_dump($arr['exists'][1][0]);
}


Expected result:
----------------
expected: sub-key 'non_existent' is set: string(1) "f"
expected: sub-key 1 is set: string(1) "o"
-------------------
good: sub-sub-key 'sub_sub' is not set.
good: sub-sub-key 0 is not set.
-------------------
expected: sub-key 'non_existent' is not empty: string(1) "f"
expected: sub-key 1 is NOT empty: string(1) "o"
-------------------
good: sub-sub-key 'sub_sub' is empty.
good: sub-sub-key 0 is empty.


Actual result:
--------------
expected: sub-key 'non_existent' is set: string(1) "f"
expected: sub-key 1 is set: string(1) "o"
-------------------
BEHAVIOR CHANGED: sub-key 'sub_sub' is set: string(1) "f"
BEHAVIOR CHANGED: sub-sub-key 0 is set: string(1) "o"
-------------------
expected: sub-key 'non_existent' is not empty: string(1) "f"
expected: sub-key 1 is NOT empty: string(1) "o"
-------------------
BEHAVIOR CHANGED: sub-sub-key 'sub_sub' is not empty: string(1) "f"
BEHAVIOR CHANGED: sub-sub-key 0 is not empty: string(1) "o"