Just to narrow the scope of the bug a bit:

$a = range( 0,9 );
$b = new ArrayIterator( $a );
 
foreach($b as $k=>$v) {
    $b->offsetUnset($k);
}

var_dump($b->getArrayCopy()); // why is 1 still around?

Sorry, I should clarify that the code above gives:

array(1) { [1]=> int(1) }

Whereas you'd probably expect:

array(0) { }

I have the same problem, used this code:

$items = new ArrayObject(array(1, 2, 3, 4, 5));

foreach($items as $item) {
	if(in_array($item, array(2, 3, 4))) {
		$items->offsetUnset($item);
	}
}

var_dump($items->getArrayCopy());

Expected result: array(1, 5), actual result: array(1, 3, 5).

Please ignore my comment above. The offsetUnset() method unsets elements using 
their index. Changing the code to this gives the expected result (0, 4):

$items = new ArrayObject(array(0, 1, 2, 3, 4));

foreach($items->getArrayCopy() as $item) {
	if(in_array($item, array(1, 2, 3))) {
		$items->offsetUnset($item);
	}
}

var_dump($items->getArrayCopy());

It seems that calling `ArrayIterator::offsetUnset` moves the internal pointer to 
the next element when removing the first index:

$a = range( 0,3 );
$b = new ArrayIterator( $a );

for ($b->rewind(); $b->valid(); ) {
    echo "{$b->key()} => {$b->current()}\n";
    $b->offsetUnset($b->key());
}

var_dump($b->getArrayCopy());

I have the same problem, are you planning to fix it?

Same problem here, as mentioned earlier: "It seems that calling `ArrayIterator::offsetUnset` moves the internal pointer to 
the next element when removing the first index"

Is there any progress on a fix?

This bug is already fixed and the report should be closed.

The original repro code prints keys 0, 2, 4, 6, and 8, which is expected. This is because when ::offsetUnset() deletes the current iteration key, it bumps the current iteration position to the next element. Then, when ::next() is called, it bumps the position forward again. So it results in iterating over every second element.

The subsequent repro code which was stated to only leave key 1 in place actually leaves all the odd-numbered keys (1, 3, 5, 7, and 9) in place, for the same reason stated above.

Just seeing if documentation for ::offsetUnset() can be updated to make this clearer...

Just submitted a PR to update the documentation on this issue...

Indeed, fixed as of PHP 7.0.0.

Indeed, fixed as of PHP 7.0.0.