Again, I don't have the specific card in front of me so I won't have its name, but one of Chrono-Ranger's Bounty cards doesn't say it destroys itself when its target is destroyed. Is that an oversight? I believe it is the only one.
You mean The Ultimate Target. I'm not sure if it is supposed to destroy itself. This bounty is pretty amazing (the best one, I think), and it *is* called The Ultimate Target, so I could see a point for leaving it (uselessly) in play after destroying the target. But it might just as well be an oversight, it does seem odd when you look at the other bounties.
This was raised in playtesting. It is intentional.
What was the reasoning abehind it? Something like there can only be one ultimate target so you will have to work to try and get rid of it. It's one reason why Jim's Hat is able to destroy bounties at the start of the turn.
You playtesters and your delicious inside information. I love and hate you.
The main reason why they omitted the card destroying itself was actually because they ran out of room on the card! However, it worked out quite well thematically, since (as already mentioned) an "Ultimate Target" should result in a victory if he/she/it is downed. It's fun coincidences like that which make me really happy that I became a playtester!