Uniwell sx8500MK2 VAT on groups

Hi,
I am trying to program VAT levels on groups, rather than individually on each PLU. In each group, I have set flag GF2 to 'affects tax' for eat-in, take out and delivery, and also set the flag for the appropriate VAT rate (ie Affects tax 1 for 20%, and affects tax 2 for zero vat).
PLU's are asigned to appropriate groups.
Receipt always shows VAT as 0.00

If I enable 'affects tax 1' in individual PLU's, the VAT displays correctly. Any ideas?

Thanks
Tim