BlockIds, ItemIds, block_id_map, item_id_map

Hello, I'm making my own "PocketMine clone"... I started with simple things... Then i tried to register custom block (lantern). Id of lantern is 463 but if i register it and run /give lantern it give me cooked salmon ://

My question is 1) how BlockIds, ItemIds, Block_id_map, item_id_map works and how to use it
2) Why some Block ids and Item ids are same
3) Why lantern item id is -208

 

Hint: 463 - 208 = 255

 

cause id 463 is already registered id in pmmp and its cooked salmon :/