Submitted by unforgiven, also found by 0x1f8b and scaraven
function initialize() of BkdLocker suppose to be called one time and contract initialize one time. but if its called by startBoost=0 then its possible to call it again with different values for other parameters. there are some logics based on the values function initilize() sets which is in calculating boost and withdraw delay. by initializing multiple times different users get different values for those logics and because rewards are distributed based on boosts so those logics will be wrong too.
This is initiliaze() code in BkdLocker:
As you can see it checks the initialization statue by currentUInts256[_START_BOOST]s value but its not correct way to do and initializer can set currentUInts256[_START_BOOST] value as 0 and set other parameters values and call this function multiple times with different values for _MAX_BOOST and _INCREASE_PERIOD and _WITHDRAW_DELAY. setting different values for those parameters can cause different calculation in computeNewBoost() and prepareUnlock(). function computeNewBoost() is used to calculate users boost parameters which is used on reward distribution. so by changing _MAX_BOOST the rewards will be distributed wrongly between old users and new users.
VIM
Add some other variable to check the status of initialization of contract.
danhper (Backd) confirmed, but disagreed with severity 
Alex the Entreprenerd (judge) commented:
