Has anyone complained to LIDL about the way their Point-of-Sale system handles the Coupon Plus vouchers?
The Coupon Plus vouchers (£2 when you spend £100 in a month & £10 when you reach £200) take a certain amount off each item purchased. So, if you need to return an item, you don't get the full amount refunded.
As the vouchers do not have a minimum spend (apart from the £2 & the £10 respectively), you should be getting the full value of the voucher irrespective of your spend.
It's not the fault of the store employees or the CSRs, just the way their PoS system has been set up. I now only use the voucher when I know that there's no chance of my returning any of the items.