That round of Eyeaduct (and every other koth map tonight to my dismay) was a classic example of the Engineer Escalation Phenomenon.
It starts with one mini sentry, and usually annoys someone enough that they'll want to get payback. So they'll go Engie. And then the first team will get annoyed, so someone else will go Engie. And then the other team gets fed up, so they pull out a full nest. So the first team does as well. And so on. It got so bad they switched the map midround because no one wanted to play anymore.
The fun of KOTH comes from the freedom the map gives you. Having three engies a team pretty much negates that.
I'm still moderately irritated at whoever's mini killed me on top of a gift. :\