It's not that hard to understand actually, we already figured it out yesterday. The crafter personal worlds have their rank set to builder, so, whatever you set the zone rank to, or whomever you add, if their rank is below the rank required by the world to build in, they can't build in it. I think Wyboth already pm'ed the admins about the problem though. They will either have to lower the required rank of the worlds, or let zone's required build rank and added builders take priority over the world's required build rank. This last option would be preferable but would require some fixing in the code and might be more difficult than it sounds.