When change order's status to "Invoice", COD's tax is deducted from grand total

[fouli86]

Preconditions

1. Magento 2.2.9
2. PHP 7.1

Steps to reproduce

1. Make a test order from the frontend
2. Process the order on the backend and generate the invoice

Expected result

1. Grand total should be product's price + shipping + COD
2. Total paid should be product's price + shipping + COD

Actual result

1. The grand total is correct
2. The total paid is product's price + shipping + (COD - tax)
3. There is a total due which is the COD's tax amount

Both products and shipping method are taxable. I have applied the fixes mentioned in #18 . Which file should I edit and how? Any suggestions?

Regards,
Fay