I have been trying to get a Business one-way flight from TXL to LHR, but it will only offer me Economy on the day I want to travel (Accross all flights). There is def business availability, if I book the same day as a return portion of a return flight, it offers me lots of availability in Business, but I cant have it if I make a one-way booking. So it seems there must be something going on with what seats are available (and for what kind of ticket!).