I also had a zombie hydra defending the kobolds that killed it.
Kobold necromancers.
This is not a bug, it's a feature. An awesome feature.
I had a titan attack a goblin dark tower, in the same year it was founded, and die during the attack - It died in 109 and later defended two different kobold caves from attack, in 331 and 340.
The last few lines of the transcribed history (I shortened the titan's name to Aba after the first time I wrote it) of the titan:
In 109, Aba Listenpoem the Permanent Years became an enemy of The Vice of Dust.
In 109, Aba attacked Stasost Jackalbeguiler.
In 109, Aba was struck down by Stasost Jackalbeguiler in Seducedsilver.
In 331, The Society of Harvests attacked Pafabagrinkus of Strulugujlirus at The Speechless Holes. Mogem Slipblows led the attack, and the defenders were led by Aba.
In 340, The Joyous League attacked Luchrulgis of Thayngin at Charmscarred. Stram Pregnantland led the attack, and the defenders were led by Aba.
The history of Seducedsilver shows that it was founded by goblins in 109 and that Aba attacked before the goblins had even made any constructions (worth noting in the history anyhow) yet. Nonetheless, they killed it.
I looked through the history of the two kobold caves where Aba supposedly led the defense in 331 and 340, but could find no other references to him in either. Both caves' defenses failed. In fact... The 340 battle says: "Attacker: Force of 19 humans. Attacker was uncontested." And the 331 battle was 38 humans and uncontested.
So! Either DF is listing a battle-leader when there are no defenders, or it is saying the battle is uncontested when it shouldn't be doing so.