Using ajax disables client side form validation, so we had the problem that certain validations we have in place (like a maximum quantity you can order certain items) wasn't handled properly.
The ajax callback kind of checks for validation errors, but all it does is then not update the cart, but it still displays a success message.
Check for errors, if so, return only those and no success message.
We also combined with with disabling IEF in custom code, because that doesn't much make sense, if you'd want to support that you'd also need to re-render and replace the whole form.
Closed: duplicate
1.0
Code