We have created an online store for our customer using Magento. All work perfectly except inventory. When a user purchase a product, the quantity isn't decreased. If we cancel the order the quantity is correctly increased.
Obviously we think the configuration is correct. We have enabled "Decrease Stock When Order is Placed" and "Manage Stock" in System -> Configuration -> Inventory. We have set product quantity for each product.
We can provide ftp access to our server and mysql access. The server is a virtual machine Windows Server 2008 with Apache Web Server.