$map = new OrderedHashMap();
$map['1 as a string'] = '1 as a string';
$map[1] = '1 as an integer';

unset($map[1]);

var_dump($map);

https://3v4l.org/ZWo3B

As you can see, after the unset of 1, it was correctly unset from the internal elements array. But incorrect key was removed from orderedKeys property. The key should be probably stored as a string and converted back when obtaining it so it behaves the same way as PHP array.
OrderedHashMapIterator needs to be adjusted as well.