1. If a cart includes a product which is exempt from VAT, Shopify is sometimes removing the VAT from the shipping cost. This occurs even if the cart also includes items which are subject to VAT.
2. Sometimes if an item which is excempt from VAT is in the cart the total VAT amount is wrong - but I can't see why. See the attached screenshot. The total VAT should be £6.97 (£5.18 from Skullcap, £1.79 on the postage).