Sales Discount with Sales Tax - Strange calculation at Sales Discount

Hi,

We are applying sales line discount manually on the sales order and the price is inclusive of tax. The system is booking tax on the price after the discount, booking receivable correctly, however, revenue and discounts are not correct. 

Please consider this example:

Unit Price 1000

Net Amount = 1000 (Inclusive of tax)

Sales Tax  = 10%

Discount (on item line) = 100

Now please see the voucher for the sales invoice.

Please see that the discount is not booked with 100 but with 91.7 (deducting 10% inclusive) and Revenue is not booked with 1000. I would like to understand why this is happening?

I tried different configuration of sales tax:

Origin = Percentage of Net Amount, Margin = net amount per line

Origin = Percentage of Gross Amount, Margin = Gross amount per line

and some others. But no luck.

Thanks in advance.