Magento – Sorting direction doesn’t make effect

there is a trick involved as Magento only allows category save on EAV structure and it differences this (if you ask for category model) in code by checking admin store scope so you have to fake the scope to be able to save the categories if you are doing this outside of admin

$currentStore = Mage::app()->getStore()->getId();
Mage::app()->getStore()->setId(Mage_Core_Model_App::ADMIN_STORE_ID);
$parent = Mage::getModel("catalog/category")->load(50);
$parent->setCustomUseParentSettings(false);
$parent->setCustomApplyToProducts(false);
$parent->setPageLayout("two_columns_left");
$parent->save();
// set the store scope back
Mage::app()->getStore()->setId($currentStore);

Take a look at this. By default Magento remembers the sorting and limit parameters in session. So what you need to do is to tell it not to. This can be done easily by adding this line

<action method="disableParamsMemorizing" />

inside the toolbar block in your layout files. So look in your layout files for all occurrences of

<block type="catalog/product_list_toolbar" name="product_list_toolbar" template="catalog/product/list/toolbar.phtml">

and add inside this tag the line mentioned above.
Clear the cache when your are done.