nCurrentHeight, a member variable in ClaimTrie and ClaimTrieCache, is not the actual current height.
It is the current height + 1 (i.e, if there is a total of two blocks including the genesis, nCurrentHeight is 2 where as the standard definition of current height would be 1) , or perhaps it can be called as the current height "to be worked on".

nNextHeight might be a better name.