They never seem to have much of a life in the vase these days. I can only assume they are "stopped" so well to maintain the sell by date, that when they hit the water they go mad, bloom instantly and finish within a couple of days.
I've always thought that daffs in a vase don't last too long anyway. Whenever I buy them, I always make sure they are very tight buds so I get a bit longer from them.