Magento Reset products per page value to default on pageload

Go to : app > code > core > Mage > Catalog > Block > Product > List > Toolbar.php

Copy this file and paste here

Go to : app > code > local > Mage > Catalog > Block > Product > List > Toolbar.php

Open this file and find this

"$limit = Mage::getSingleton('catalog/session')->getLimitPage()" aroung 745 line no.

replace with

$limit = Mage::getStoreConfig('catalog/frontend/list_per_page');

After completed above steps Please remove cache

Best of luck