Just that really. 300cm is the norm, not 250cm.
DD had been banging on about revamping her room for a while so we popped into IKEA in the Netherlands (Delft - cheap lunch with our UK Family card and a great organic bakery too) on a cold wet day.
All the labels were in Dutch AND English. We didn't particularly want to cart a load of curtains around Europe with us so just checked they were sold in the UK...it didn't dawn on me that the lengths would be different. DD's curtains need to be 260cm+.
I wonder when IKEA UK shrunk their curtains (we definitely have some longer sheer ones but they've been in the attic for a while).