A question about CI cart

[eluser]WanWizard[/eluser]
If you insert a cart item, the internal item key is calculated using the item ID and the options array. If the calculated key already exists, it will be overwritten.

If you want to update the quantity, use the update() method. It still doesn't allow you to increment the quantity, you'll have to extend the Cart class and add an increment method (or modify the update method).