I can clarify this a bit. If you waypoint away before something dies and it dropped loot, you won't immediately get it. If you return to the area, you will get the loot as soon as you can see it. It will basically pick up all loot you can see.
The exception is WvW, since loot bags always spawns at your feet. If you waypoint, the loot will spawn at your location and should get immediately picked up.
If your inventory is full when something drops, it will be left on the ground and you will have to pick it up manually after you clear out some space.
Edit: Unrelated note while I'm here, that purple star is placeholder (I reused the living story quest marker while I wait for the art request). It should have its own icon at some point.