This is a common bit of confusion with the decay system: Each item decays independently. This means that items received, say, 60 days ago will continue to decay, while the new item should remain at full value (at least until it's 45 days old).
If you look at his item history (on the member profile page), you'll see that the new item received SHOULD still be at full value, while the other items that haven't reached the 25% minimum, will continue to decay.
What I am a bit confused about is that on the raid the 11/22/07 he earns 18 dkp - at the same raid he spends 35.
Now when he used the 35 dkp on the item he used up all his dkp. But the new 18 he earned at the same raid is also appearing to decay.
When I look at his profile it shows as having full value as the item - but if they have the full value still - then it means that his old dkp are continueing to decay - leading to his new 18 getting decreased ?
Also another question - can the dkp pool go into minus? what I mean is, if a member at any given time have say 20 dkp which is decaying atm, then spends these 20 dkp on an item - what will happen to his dkp pool - will to just go to 0 or will it continue to a negetive value ?
It will continue to decay into the negative until the raids or items that are decaying are at their maximum decay.
So, what you see on his page is that he recently earned 18, but some things are still decaying for him. It doesn't stop when we starts raiding again, every item decays at the same independent rate.
