It doesn't happen often, but when it does it's very annoying because often that means you can't apply any other promo code, such as sitewide discounts. Recently, I have come across egiftcards from Easi and Adidas (obtained from Medibank) as culprits.
Any others?
The aim is to help others work out the true value of those egiftcards.
Maybe an asterisk on the e-gift wiki
.