Every time someone has complained about this and actually linked to a game when this supposedly happened, it has been confirmed that they misunderstood the rules. As noted above, but stated another way, you don't *always* get another turn when someone triggers end game and it has nothing to do with whether you could possibly win. You only get another turn if you haven't already had as many turns as the person who triggered the end game. If you are before them in turn order, you do not get another turn. Period.
Edit: I see you are the same person who complained about this in the Splendor forum on Nov. 28 and it was explained there. This is not a bug. DomitienAW even pulled up a link to the game they thought you were referring to (because you didn't do it yourself) and asked you to confirm it was one of the games you were confused about. Despite them going out of their way to help, you didn't respond.