Fixes problem with loading a product list block while there is a "product" entity set on the registry

product_list_block_fix.diff

Index: app/code/core/Mage/Catalog/Block/Product/List.php
===================================================================
--- app/code/core/Mage/Catalog/Block/Product/List.php
+++ app/code/core/Mage/Catalog/Block/Product/List.php
@@ -71,7 +71,7 @@
                 // if the product is associated with any category
                 if ($categories->count()) {
                     // show products from this category
-                    $this->setCategoryId(current($categories->getIterator()));
+                    $this->setCategoryId(current($categories->getIterator())->getId());
                 }
             }