HI Robin,
First point, I am working with R&D to clarify whether a recalculation should have occurred when the order was moved from Resolved to Pending Invoice status. Hopefully we can find out what is happening to not set it to zero value in these cases.
For why it was populated in the first place, it looks like this may be done prior to changing the billable type flag to otherwise as the information I currently have is:
When a user decides to send an order to the invoice (later or to auditing), the order goes through the order completion process and the prices are calculated. The order is completed and is waiting for invoicing (batch). At this stage, the order can be modified and its new price can be different, but the Audit queue will still show the old price, until the order price is recalculated.
It is this last part that I am investigating with R&D to find out why the recalculation did not set the values to zero when going to the invoicing module.