AP Invoice - how to track through tax rules triggered when document created

Hi,

I have an issue for a customer using R12.1.3.

Since applying a patch on a test system, there's an invoice - shown below - and there is a £30 Freight line (line 2 below) - but a 20% Tax Rate is being applied to against that Freight line (line below - value of £6):

If we scroll across the lines to the right a bit:

We can see that the Tax Classification Code for the Freight Line 2 = "GB NO VAT", but somehow the Tax Rate Name for Line 4 has  value of "GB VAT STANDARD".

The Tax details for line 2 of the above invoice appear as: