Yes, another trick from the Shattered Sun Pendant of Accumen. IT'S NOT A REPOST, READ THE WHOLE THREAD.
After some extensive tests on the Pendant, I confirmed that you don't get flagged if the proc hits someone that's already flagged.
What does that mean?
You can interrupt casts, drinkings and bandages of the flagged person. You can also just add up some damage (and eventually get a KB while on a huge World PvP situation ) while being immune to ganking.
Will post a Screenshot as soon as I can get to.
EDIT: Screenshot, you can check the Combat Log, my name being shown and not green (unflagged), the damage and the target on the flagged person.