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How It Should Be Working
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In terms of all crafting ingredients, those should be shared: anybody picks up anything, and you can all use it. That goes for the tier orbs as well as the other stuff like raw crystals, etc. That's how you can quickly "catch up" to what the other players are doing on a continent, and how each player can customize their own spell loadouts, etc.
In terms of building materials (cedar logs and granite at the moment) and guardian power scrolls, those are things that are shared between all players: if anyone uses those, then nobody else can. But of course that's not a problem, because these always benefit everyone anyway.
What Might Be Happening
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The most obvious thing is that this could be a bug. However, in older continents on older worlds, it could also be that those tier orbs and resources were spent before we added in the logic to let each player have their own copy of them. In that case it's not a bug, it's just an unfortunate side effect of an old continent on an old world from before that change was made to MP... I'm not sure, 3 or 4 weeks ago.
Regarding the tier orbs not being reduced, I think that might be a MP permissions thing but I can't recall for sure. As in, it might be that server admins have to grant access to those specifically, because otherwise griefing players would be extremely possible. Or that might be a bug, I'm not sure on that one. Keith will know better there.
EDIT: Ninja'd.