This is because no movement map data exists for that place. In creature_proto under custom_flags set it to 32 and it should ignore pathfinding data.
Code:
enum CustomFlags
{
CREATURE_CUSTOMFLAG_CANTDIE = 0x1, // 1
CREATURE_CUSTOMFLAG_IMMUNE_TO_CREATURE_DAMAGE = 0x2, // 2
CREATURE_CUSTOMFLAG_CANT_REGEN_HEALTH = 0x4, // 4
CREATURE_CUSTOMFLAG_NO_LOOT = 0x8, // 8
CREATURE_CUSTOMFLAG_VEHICLE_COMBAT = 0x10, // 16
CREATURE_CUSTOMFLAG_NO_ADV_PATHFINDING = 0x20, // 32
CREATURE_CUSTOMFLAG_NO_RETURN_AFTER_COMBAT = 0x40, // 64
CREATURE_CUSTOMFLAG_NO_ADV_VMAPS = 0x80, // 128
};