Some odd things happen sometime - I can have a list of say 12 missions available from a faction I am friendly with, I accept one, and a certain bunch of 5 or 6 are still on the board, but have moved to unavailable due to lack of trust. So far I have just assumed that is because they trust me a little less, nervously awaiting to see if I complete the mission I accepted, and if I am only just friendly with them, that might be enough to tip the scales. Could be something similar here, would certainly be interesting if ship type does make a difference too, and could make some sense, how well armed you are might increase or decrease their faith and worry that you'll be able to complete a mission for instance.
Or it could be a bug, in both cases. Hmm.