probably because treaty is actually allying during the span of treaty.
and since its in post imperial age, the unique tech is already researched and treaty hasnt expire at the time of tech research completion given future enemy (current ally) access to kipchak and stays that way even with treaty expiring.
AI does weird things too that will still trade with enemy market after treaty expires, probably an overlook in the game design, or simply a limitation they couldn’t solve.
try this, have your game starts in imperial rather than post imp, you and your friend will be enemy, 1 minute treaty. wait till treaty expires THEN research cuman mercs to see if enemy still have access to it.
Yeah, no big deal, i get that. I just joined a random lobby where someone wanted to play with these settings and I was like “well, guess I will try and see what this turns into”… completely steamrolled him… but well noticed that little detail during the match
As stated before: I am not sure if this behaviour is intended or not. It migth be totally fine, but seemed unintentional in the first moment, but migth be totally fine due to the explanation of @WoodsierCorn696, and even if it is unintended, since it is afffecting almost noone, I would say: Put it on the bottom of the to do list