The standard should be available to caputre for several tics after a foe is slain. If you kill your oppoent and they quickly log off, something they can ONLY do because you won, you should still have the opportunity to collect their standard.
As it is now, you kill them, they log, and everything is safe. This means that "winning" in pk equals losing in CTF, in several situations.
If you just killed them and they log off, you should be able to cap the standard as it is now. Please provide a log on prayer if this is not the case, showing the time that has passed since you last engaged / killed them.
You stayed in combat with the guard till it died? (Cabal closing up message =/ you can't capture any more)
I've been in combat with a cabal guard 4 or 5 ticks after someone leaves, and still been able to capture the standard. You just have to be in combat with the guard before and while the enemy quits out.
Re Jibber: You don't have it exactly right, however the standard should be cappable in the situation described above.
Well, at least I was close. I just know that that's the only time I can take a standard when someone from a vendetta'd cabal quits.
I've taken standard in the past where the opponent logged out before i engaged with the cabal guard - but i managed to kill the guard in a few tics. I've had other situations like jibber has mentioned where I have killed the opponenent - they have run back to their corpse, grabbed whatever was left and run out, and i kill the standard next tic and i can't get it - I've never been able to pin down what the circumstances are that make it work.