I was planning a trip to Helsinki in April and found an expensive quirk in their website
Go to Finnair.com.
Enter departure from Dublin to Helsinki
Apr 7th returning Apr 10th. = 333 euro
Now do the same thing but enter returning Apr 9th. The website reports that there are no available seats and offers the same flights as above but at 857 euro, a 500 difference and doesnt offer any economy level fares
Reason is all the cheaper fares have a minimum stay requirement of 3 days .. so if you look for under 3 days it forces you to the higher €800+ fare level (which is still an economy fare by the way) ... but it's silly that by then looking for alternate days it finds them but doesn't understand that it can sell you the flights on those days for less as it's now a more than 3 day stay.
Not the best booking engine really by the looks of it.