Minecraft wiki entry for Development_versions, associated text: 13w12~ refers to two debug snapshots for Java Edition 1.5.1 that attempted to fix an issue with the frame rate dropping significantly when using smooth lighting. The first debug snapshot was unsuccessful,[2] while the second debug snapshot was successful in fixing this bug.[3] The first snapshot was released on Mojira as a "temporary snapshot",[4] which is why these snapshots do not follow regular naming conventions.