It is a good feature that a customer must select an option before a product can be added to a shopping cart but my product is showing "Out of Stock" even if only one size is not available so the customer may think everything is out of stock.
For example in the attached screen shot I am only out of stock for one size but it displays out of stock.
The default behaviour should be 'Available' if there are any sizes available.
This is well-known bug. Please contact CS-Cart support team for fix