The thing is this. When a zone has a lot of content, objects are scattered across the zone according to specific rules. Mines - 1 ore and 1 wood are mandatory within direct path distance (i.e., by flight) of 1 day from the town, while the other mines are spread across the zone further away from each other, and usually get stuck at zone borders. With such a number of mines as on Jebus Cross, it's quite likely that a mine will be placed right on the border and will cut through it, and naturally, no guard is provided for it, because from the RMG's perspective, it's a solid wall; one algorithm doesn't know what the other has done. As for the road network, I think it was laid out initially, but it's either a border bug (sometimes a road goes right through a border, even on other templates) or there was a passage there, but the mine overwrote even the passage guard.