multiple bugs report:
After conquering Mairaath it continues to spawn fleet "The Vengence of Mairaath", which fact it did not spawn until after I conquered the planet and the faction has zero markets. This fleet is hostile and consists of a fleet that can easily wipe out a space station and mid-game fleet without losing a ship.
After terrorizing me for two years, I was able to defeat it with my entire fleet and a battlestation, at which point it respawns nearly instantly magically from a planet that is under my control (Mairaath)
After joining the faction it was previous allied with for other reasons this fleet became an ally, not 100% sure these things are connected.
In addition, the former structure under the old regime known as the "Elite Mayasuran Guard HQ" which vanishes after you take over the planet, still continues to cost me 5 ship hulls, 6 heavy armaments, 5 fuel and 5 supplies (found examining the commodities tool tip), which is really screwing me.
edit:
with some help and console command mod I was able to "remove_industry" while docked which deals with extra demands.
edit2:
When talking to the guys in bars selling production credits specific and exactly the same Mayasuran ships hulls are listed 4 times. Is this related to the reason I feel like I'm always finding Mayasuran blueprints everywhere over the time of several runs?