A couple of turns before I was ready to carry out my attack plan against the Thalans, I noticed a fleet of 3 Thalan heavy fighters are cruising around my home planet. Now, my ships are all set up to attack along the borders, and I don't have the resources to build ships fast enough to take them out before the invasion, so I tried to buy them. I noticed they are all "M5-something or other", so I go into the trade screen, and along with the ships they had for sale were three heavy fighters, "M5-something or other"(and only three), so I trade my dip translators, and some worthless techs and a little money, and bought 'em.

HOWEVER. When I got out of the trade screen to go send my new ships to the front lines, it had sold me three other ships! The original fleet was still there, and the three ships I had purchased were deep in soon to be enemy territory. What gives?

They were indeed heavy fighter "M5-something or other", and I am assuming what happened was that due to low espionage levels I would not be able to know about all the ships that an opponent has and bought the wrong ships, but how could I possibly not know about three ships parked on my front lawn?

Has anyone else tried buying a particular ship and succeded or failed? Is this indicative that the AI will not sell ships in a fleet, or does not offer all ships in the trade screen?