See map above. Replace the impenetrable rock where the brimstone is using the mass replace command (ctrl + click).
Bug: If player placed impenetrable rock is touching the map edge (uneditable impenetrable rock) and you use a mass replace command on the player placed rock, then the map edge is treated as part of this and it causes all other impenetrable rock that is touching the edge of the map to be replaced.
Solution: Map edge shouldn't be considered part of the map (even though it shows at impenetrable rock) and thus shouldn't be included in the mass replace command.
Customer support service by UserEcho