gistfile1.php

    public function extract()
    {
        if ($this->object instanceof Traversable) {
            $this->object = ArrayUtils::iteratorToArray($this->object, false);
        }

        if (!is_array($this->object)) {
            return array();
        }

        $values = array();

        foreach ($this->object as $key => $value) {
            if ($this->hydrator) {
                $values[$key] = $this->hydrator->extract($value);
            } elseif ($value instanceof $this->targetElement->object) {
                // @see https://github.com/zendframework/zf2/pull/2848
                $targetElement = clone $this->targetElement;
                $targetElement->object = $value;
                $values[$key] = $targetElement->extract();
                if (! $this->createNewObjects() && $this->has($key)) {
                    $fieldset = $this->get($key);
                    if ($fieldset instanceof Fieldset && $fieldset->allowObjectBinding($value)) {
                        $fieldset->setObject($value);
                    }
                }
            }
        }
        
        // Recursively extract and populate values for nested fieldsets
        // PROBLEM: Since this is a collection, the elements in it are fieldsets, so they get extracted here
        foreach ($this->fieldsets as $fieldset) {
            $name = $fieldset->getName();
            if (isset($values[$name])) {
                $object = $values[$name];

                if ($fieldset->allowObjectBinding($object)) {
                    $fieldset->setObject($object);
                    $values[$name] = $fieldset->extract();
                } else {
                    // PROBLEM: childFieldset is in our case the nested collection, which also implements FieldsetInterface
                    foreach ($fieldset->fieldsets as $childFieldset) {
                        // FIX: Skipping collections solves the problem, but does not seem to be the right way to go
                        if($childFieldset instanceof \Zend\Form\Element\Collection) {
                            continue;
                        }
                        $childName = $childFieldset->getName();
                        if (isset($object[$childName])) {
                            $childObject = $object[$childName];
                            if ($childFieldset->allowObjectBinding($childObject)) {
                                // Fatal Error: Now what happens here is, we attach the childObject, which is a traversable object of the
                                // nested fieldset to one of the elements(fieldsets) of the current collection - BAM 
                                $fieldset->setObject($childObject);
                                $values[$name][$childName] = $fieldset->extract();
                            }
                        }
                    }
                }
            }
        }

        return $values;
    }