The €5 off €25 voucher when you purchase clothing/homewares seems to be back as a pre-christmas offer, in some stores at least. I unexpectedly got one the other day in the Swords Pavilions store.That's a very old offer and long since finished AFAIK. Certainly can't see it applying at Christmas when the spending is wild in Dunnes.
It does indeed, very odd too. I always find that the local staff don't know an awful lot about the vouchers and how they work other than the basic rules.