You are looking at the result of a change that is only 15 hours old as I write this. Previously, there was no connection of any type between sales orders and invoices, except that a sales order reference number could be carried over to a sales invoice. The Invoiced column was just added as the first step in developing a more comprehensive status monitoring capability.
What you see is exactly correct. The Amount on the sales order is 10.00. The amount Invoiced, due to withholding tax, is 9.00. For now, the Sales Order tab will not give you complete status information. Until yesterday, it would not have given you any status information at all. This concept is still in the ideas category: Status of quotes, Sales Orders and Purchase Orders Idea - #40 by lubos.