This happened to me in my current game as well, the Korath surrendured to the Drath and the Yor surrendered to the Thalans, both happened within a few turns of war being declared, I doubt that they even had any battles...

Playing as the Korx I am now the last Evil empire  , I was already at war with the Torians a few turns after the Yor surrendered Three races declared war on me at once, then the remaining three declared war the very next turn. Even the Krynn who I had decent relations with are now enemies. Im holding my own and making small advances against the Torian/Krynn/Thelans, mostly because thier invasion attempts have so far been pathetic(multiple fleets of unescorted transports...)

The 'your transports are too much of a threat, I declare war' thing seems to be outa wack as well... races on the other side of the galaxy used that as a reason, it would have taken 30 turns for my closest transport to find one of the Terran worlds...

I wish they got rid of these game ruining surrenders,or at least made it an option.

also, don't forget, i read that the IA hasn't been worked on much YET for DA, that is coming now. so they will be better.

that happened to me also but it was with me i declared war on the yor with the drengin they surrendered to the drengin after i attacked them

Yea, I just had a wierd game... I had both the Drengin and the Drengin offshoots on a tough setting. The drengin were at war with their offshoot, and were under cultural attack by the Drath. Togather, both the drengin clans had a pretty sizeable hunk of the galaxy. Then, without warning, the Drengin surrendur all their territory to the Thalans, and their offshoot clan surrender to me. I still can't figure it out.

I have seen two strange surrenders in my last game. Unfortunately, I do not remeber the races involved, but I do remember that afterwards two of the oponents had basically doubled almost all their ratings (economy, industry,...). Thus, a balanced game turned out quite unfair.

I wonder if this is supposed to work like this.

I think their should be some penalty on the output of the surrendering planets reflecting revolting people or racial tensions (even ig alignement is similar), maybe it could be implemented as in MOO2 for example.

I have removed the Drath Legion (Super Manipulator), disabled surrendering, and sold all rival civilizations the first three levels of military techs, just because of this particular bug.
I and others have noted this before. I had a topic called 'pacifist surrender monkeys.' The problem seemed to be keyed to the excess priority that was given to colonization techs. I have had major civs go midway into the game and research no military tech at all. This has lead to a rash of surrenders early into the game. Civs seem to be quite willing to declare war with no military whatsoever. Then there seems to be a check every turn for a civ at war to see if their military has been destroyed. Add the Drath's super-manipulator ability which gets everyone to declare war on everyone else and you get a huge amount of wierd surrenders.
Now, if you check the Developer's journals, they have been working on getting the research into the proper order. I know that there is some awareness of the surrendering problem because the added the option of no surrenders into the game set up.
What I don't know is what has been fixed in the Gamma and what will still be there when Dark Avatar is released.

Scincerely,
Scintor