This was a downright horrible thing QuickBooks to do their customers.  I wondered why one of my clients hadn't paid an invoice last month.  They had been trained for past few years to receive the invoice as an attachment.   Your surprise change led to them not seeing invoice.  

That is a horrible way for Quickbooks to treat customers.  We should not be surprised like this.  One more reason I absolutely do not recommend any of my friends or clients start using your product.  Once we've  used it for years, we have to weight this kind of crap against inconvenience of starting over.  As a potential new customer, my advice to them is to shop elsewhere.