A change has been made in how Teapplix represent sales tax when exporting to QuickBooks.
Starting from 3/8/2011, all exports to QuickBooks that are "taxable" will have the "customer taxable" bit turned on. Orders with no tax will have "Customer taxable" bit turned off.
Before 3/8/2011, Teapplix exports orders by choosing among 2 different sales tax items: one with your state rate, the other with 0 tax rate. If an order has 0 tax, then Teapplix chooses the 0 tax rate item.
This old method requires you to configure a sales tax item with 0 rate. This actually triggers an warning when you do tax related reports in QuickBooks.