Now that the game is finished, I'd like to ask for this rule to be clarified: "no liberating cities to a civ you are at war with (except in peace deal)"
The rule was in place before I played any HoF or SGOTM games, so to me that's a rule that always has been there in that form. I've read it by the literal meaning of the words, meaning no city gifting between getting into a war and signing a peace treaty. By definition, a ceasefire agreement does not end a war.
The parties involved in a ceasefire temporarily stop fighting, but formally they are still in a state of war.
However, that's the real world dictionary. I now see that the civ 4 dictionary appears to be very different... After choosing cease fire, you have to declare war to resume hostilities, you get more diplo penalties for "you declared war on us/our friend" and perhaps most importantly, you cannot even sign a peace deal anymore. And just now I noticed that the logs even say that you have made peace. So the Civ4 ceasefire is not really a ceasefire, it's more like a peace treaty with fingers crossed behind your back. It seems this is how the rule has been applied, seeing that several teams liberated cities during ceasefires to get diplo points for AP votes or gifting the beach resort.
If city gifting is allowed also after a ceasefire, then I think the wording of the rule should be changed to clearly indicate that it is. Currently there is an ambiguity in the rule, leaving it up to interpretation whether a war ends with a ceasefire or not.
Then one could still ask if gifting after a ceasefire should be allowed. kcd's explanation of the rule, from when it first was introduced, indicates that this was not the intention:
http://forums.civfanatics.com/showpost.php?p=12368724&postcount=53
It seems like quite an exploit that you can get any former war target to friendly status without much effort by repeatedly liberating several cities on consecutive turns. However, if it weren't allowed, then it would cause trouble after taking a ceasefire, because you cannot sign a peace treaty anymore without first declaring war again. Maybe one solution would be to instead require a minimum amount of turns to pass between liberating a city and recapturing it. But maybe this would come with some other problems that I can't think of straight away. Discuss.