You are using Dataset incorrectly. When I said you would need to save using code, I meant that you would need to use wixData.save() , and NOT the dataset.save() function. Your second dataset is empty, since none of the fields in the form are connected to it (because they are connected to the first dataset). So when you save, it saves an empty item.
You will need to use create an object containing the fields to save in the collection, and then save using the wixData.save() function,. See the sample code snippets in the wixData.save() API .