I think I already bought that destination, but when I had to send an L plane to maintenance, I had to buy it again.
And same in IAD for XL planes.
It cost me 20.000 plus 30.000 now 
Happened to me too.
Bringing this up again beacuse it just happened to me on PRG, for buying FRA. Im sure i had it before since its as far as i know the only maintenance base for M planes out of PRG and i already sent planes for maintenance in the past. Does anyone know why this happens?
It happened after the Updates, so maybe some settings locally or serverside were corrupted. @shill: have you received similar reports?