When a pass of CreateTransaction fails to select enough bitcoin to meet the nFeeNeeded the next pass through may select a far smaller collection of inputs.  Currently it will continue to use the old fee amount based on the larger set of inputs, which can cause a non-trivial over-payment.

This may be the cause of the behavior reported here: https://www.reddit.com/r/Bitcoin/comments/5ltw5n/bitcoin_core_v0131_sends_enormously_high_fee/

Long ago fixing this was tricky due to a catch-22 between signing the transaction and knowing how much fee was required.  But after #9465 the whole algorithm will run using a dummy signature, so when there is already a change output fixing up the fee after finding a sufficient transaction should be a matter of a ~2 line change.

{
        nWalletVersion = FEATURE_BASE;
        nWalletMaxVersion = FEATURE_BASE;
        fFileBacked = false;
        nMasterKeyMaxID = 0;
        pwalletdbEncryption = NULL;
        nOrderPosNext = 0;
        nNextResend = 0;
        nLastResend = 0;
        nTimeFirstKey = 0;
        fBroadcastTransactions = false;
    }
    std::map<uint256, CWalletTx> mapWallet;
    std::list<CAccountingEntry> laccentries;
    typedef std::pair<CWalletTx*, CAccountingEntry*> TxPair;
    typedef std::multimap<int64_t, TxPair > TxItems;
    TxItems wtxOrdered;
    int64_t nOrderPosNext;
    std::map<uint256, int> mapRequestCount;
    std::map<CTxDestination, CAddressBookData> mapAddressBook;
    CPubKey vchDefaultKey;
    std::set<COutPoint> setLockedCoins;
    int64_t nTimeFirstKey;
    const CWalletTx* GetWalletTx(const uint256& hash) const;
    
    bool CanSupportFeature(enum WalletFeature wf) { AssertLockHeld(cs_wallet); return nWalletMaxVersion >= wf; }