Tax Rate/Area TXA1 on Business Unit Master

When a tax rate/area is specified on a BU master (TXA1), will that tax rate/area default when entering an A/P voucher?  The following is per an FAQ document but I can't get it to work.  Thanks.

Question 9: Why is the value populated into the Tax Rate/Area (TXA1) field on a new voucher different than the value defined for the supplier?

Answer 9: The system uses the tax rate/area associated with a business unit, if one exists. If a tax rate/area is not associated for the business unit, then the system uses the tax rate/area for the supplier from the Supplier Master (P04012). The system uses the tax explanation code from the supplier record regardless of whether it uses the tax rate/area from the business unit.