Problem: When updating a invoice created under the old Quickbooks 2006 (converted on April 30, 2009) a problem may arrise. If the qty or rate fields are changed, all the amount values change to weird values, and the PST and GST become zero.
When updating one of these invoices, make sure to change the tax code to something else and then back to the intended code (ex. change from S to G and back to S). This needs to be done only for the line item being changed. All the values should calculate fine.