It seems like it would be fairly easy for the game designers to make each character have a solitary vault where items would be non-transferable between characters, but the fact that it is not, AND you may often receive rewards/loot that is for another character type seems to prove there's an incentive here to in fact use the vault as well as create additional characters. This was meant to happen. Just like you cannot remove bounties from your inventory I.e. Exotic bounties, whatever, that too was seemingly meant to happen, not that I'm suggesting everything in this game that can happen was meant that way, we obviously know we are not glitching nor abusing the system in doing this