When you are in a customer and click a specific invoice it changes the breadcrumb links at the top to Invoices-INV##, so if you click back one level to invoices you don't go to that customers invoices go to All invoices. Then you have to go back to Customers and find that customer again to get back to a list of their invoices.

I know this sounds trivial because I could just hit the browser back button, but it gets me everytime and wastes a lot of clicks.