Abuse 1

Tested for more diplomacy trade and I've found another 2 game breaking abuses. First, I've traded an empty (just colonized) planet with the AI, and I managed to get all their techs plus about 4k+ credits per week. Even though the AI do not have enough credits to pay me, I was properly paid and the AI was properly deducted. Hence, over just a few turns, the AI is effectively bankrupt (20k+ in debt) and all their planets are shut down for the rest of the game to repay the debt (mouseover their planets shows that the production and research are all 0). While I, having 4k+ credits per turn even before turn 100 have effectively won the game.

I played on to check if the AI will break the treaty or not, but the AI didn't break it over normal gameplay. The treaty was only broken after I've reloaded the game as I was no longer paid then (Note: technically, I cannot confirm if the treaty was broken since I could not open the treaty screen at all. See CTD 1 below). After reloading, I still can trade another empty planet with another AI to get a new 4k+ "subsidy" though. 

Abuse 2

I've also tried to trade an empty (just colonized) planet with another planet from the AI, and it was accepted as long as I add another 10bc on top of the transaction. For example, I've just colonized a size 4 planet and traded it for another size 12 mature planet from the AI (as long as I top up the 10bc). This was traded with a normal, non-bankrupt AI, so it is a very lopsided trade.

For more fun, I've bought all the colony ships from the AI (cost about 200+ bc each, quite costly in early game), colonize any nearby planet, and then trade the new planet with their mature planet. Effectively, I've got a mature planet for the cost of just 200+ bc. In addition, I also can trade a empty planet for a mature planet, raze all their improvements, and then trade the razed planet for another mature planet, ad nauseum. Effectively, I can raze all the planet improvements of the AI with the cost of 10bc in each trade.

CTD 1

Using abuse 1, I can no longer open the treaty screen as it resulted in a CTD. I suspect that the CTD is related to abuse 1, since I can open the treaty screen just fine in previous game and also in early game (before I use abuse 1). Perhaps opening the screen will trigger the game to check for invalid treaty and ended up crashing the game when an invalid treaty was found (which abuse 1 certainly qualified for. The AI is paying an amount of money that they do not have).

This occur even after reloading the game, and I no longer use abuse 1. So, as long as I've used abuse 1 before, opening the treaty screen will result in a crash.

CTD 2

CTD 2 is not relevant to the abuses above as it is caused by unlocking the persuasion ideology. But, it happened in the same game above, so I'm reporting it here as well.

I've submitted the savegame and the ticket is #VHB-366-90076. Thanks.