Doomsday Engine

Build 1598, OS X 64-bit.

Null pointer access when returning to Seven Portals from Guardian of Fire:

thread #85: tid = 0x14f59c, 0x000000010353b6ba Doomsday`SectorCluster::sector() + 26, name = 'CallbackThread', stop reason = EXC_BAD_ACCESS (code=1, address=0x0)

frame #0: 0x000000010353b6ba Doomsday`SectorCluster::sector() + 26
frame #1: 0x000000010353f883 Doomsday`SectorCluster::Instance::map(int, SectorCluster*, bool) + 115
frame #2: 0x0000000103543342 Doomsday`SectorCluster::Instance::~Instance() + 562
frame #3: 0x000000010354218e Doomsday`SectorCluster::Instance::~Instance() + 14
frame #4: 0x000000010353b812 Doomsday`SectorCluster::~SectorCluster() + 34
frame #5: 0x0000000103526d44 Doomsday`de::Map::Instance::~Instance() + 500
frame #6: 0x00000001035265be Doomsday`de::Map::Instance::~Instance() + 14
frame #7: 0x0000000103520b92 Doomsday`de::Map::~Map() + 34
frame #8: 0x000000010354f26d Doomsday`de::WorldSystem::Instance::changeMap(MapDef*) + 109
frame #9: 0x000000010354f1e5 Doomsday`de::WorldSystem::Instance::changeMapWorker(void*) + 21
frame #10: 0x0000000104ae21e6 libdeng_legacy.dylib`CallbackThread::run() + 38

Savegame attached, although issue does not seem to be (easily?) repeatable.