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.

{
        {
            LOCK(cs_wallet);
            std::map<uint256, int>::iterator mi = mapRequestCount.find(hash);
            if (mi != mapRequestCount.end())
                (*mi).second++;
        }
    }
    void GetScriptForMining(boost::shared_ptr<CReserveScript> &script);
    void ResetRequestCount(const uint256 &hash)
    {
        LOCK(cs_wallet);
        mapRequestCount[hash] = 0;
    };
    
    unsigned int GetKeyPoolSize()
    {
        AssertLockHeld(cs_wallet); 
        return setKeyPool.size();
    }
    bool SetDefaultKey(const CPubKey &vchPubKey);
    
    bool SetMinVersion(enum WalletFeature, CWalletDB* pwalletdbIn = NULL, bool fExplicit = false);
    
    bool SetMaxVersion(int nVersion);
    
    int GetVersion() { LOCK(cs_wallet); return nWalletVersion; }