@MarkAndrew,
I now see the problem.
When you void a supplier invoice, the underlying Delivery is NOT voided. This has to do with when using the supplier invoice in the right panel, you can select which deliveries is going to be included in the supp invoice.
Therefore voiding a complete direct supp invoice ( and a built up supp invoice from the right panel) will not be done and it will Always require a 2 step operation.
1. First void the supplier invoice.
2. And now void the PO delivery.
Although most of the time it could be done to void both the supp invoice and the receive, it would be dangerous to do this and in several cases it qould not be desirable.
So I will leave the operation as is.
The wiki has been update here.
/Joe