Invoice problem

We are having problems with Invoices and Tax Codes. We have a Tax Code called 20 CEE with a rate of 20%. There was an Invoice entered with an amount of 49,147.03 would mean the tax amount should be 10,812.46, istead the calculated tax amount is 8,862.58.

I have had a look at the tax set-up and everything looks ok and the Vendor has been reviewed and everything looks ok. Anybody have any ideas why the tax is been calculated incorreclty.