If a player plays Grain Sales to Soviets in Headline Phase, pulls UN Intervention, and plays it instead of returning it, is taking back such a move allowed under mutual agreement?
I analysed the wording and the spirit of the rules. They say that a known avoidable bug must not be exploited and that taking back moves is not allowed even under mutual agreement unless it is done to repair the damage caused by the engine bug.
Offering an experienced player an opportunity to play a card in a way he is not allowed to do may cause him use the opportunity involuntarily. This is not a typical exploit and this is not a typical misclick. This is an action which is forbidden by the rules but allowed by the engine. So, this certainly break the rules and, therefore, may lead to immediate game ending due to it, but such an ending can be easily treated as a damage caused by the engine bug which is the only exception to the no-taking-back rule, and I am into such an interpretation.
Yes, this is allowed if both players agree to it. If any player disagrees taking back is not allowed and USSR player has the right to claim immediate victory.
I will add this to the rules for the next season but this interpretation is binding for future games. Please note that this does not change anything for players who disagree with my interpretation as they may easily disagree for a takeback, therefore I consider it fair to change the rules this way in the middle of the season.