In app/code/core/Mage/Wishlist/controllers/IndexController.php
-> public function cartAction()
replace this:
if ($item->addToCart($cart, true)) {
with this:
if ($item->addToCart($cart, false)) {
or directly remove the second parameter (true), because this calls app/code/core/Mage/Wishlist/Model/Item.php
-> public function addToCart(Mage_Checkout_Model_Cart $cart, $delete = false)
(@param bool $delete delete the item after successful add to cart).
The above is working only when "Add to cart" button is used. For button "Add all to cart" you should replace in app/code/core/Mage/Wishlist/Controller/Abstract.php
-> public function allcartAction()
this code:
if ($item->addToCart($cart, $isOwner)) {
with this:
if ($item->addToCart($cart, false)) {
Or you can just comment/remove $this->delete();
from app/code/core/Mage/Wishlist/Model/Item.php
-> public function addToCart
.