in v0.12 https://github.com/bitcoin/bitcoin/pull/7081 (by @luke-jr) was merged adding `-bytespersigop` (with default of 20).

this is preventing simple bare multisig transactions from being accepted into mempool when the size is < 400 bytes.  
eg; https://gist.github.com/rubensayshi/ac4f617207f7a50559e85d61c05800be

from 1-of-7 and onwards they are accepted because the ratio of bytes:sigops is high enough.  
also having 2 or more inputs will work because it again tips the ratio of bytes:sigops over.

the reason mainly being that `GetLegacySigOpCount` calls `GetSigOpCount` with `fAccurate=false`.

It looks like changing `GetLegacySigOpCount` to use `fAccurate=true` would cause side effects in the few other places (`ConnectBlock`, `CheckBlock`, `CreateNewBlock`) and simply adding `fAccurate` as arg to `GetLegacySigOpCount` would affect the value stored in `CTxMemPoolEntry.sigOpCount` which in turn affects a bunch of other things.

RegisterWalletRPCCommands(tableRPC);
#endif
    nConnectTimeout = GetArg("-timeout", DEFAULT_CONNECT_TIMEOUT);
    if (nConnectTimeout <= 0)
        nConnectTimeout = DEFAULT_CONNECT_TIMEOUT;
    
    
    
    
    
    
    if (mapArgs.count("-minrelaytxfee"))
    {
        CAmount n = 0;
        if (ParseMoney(mapArgs["-minrelaytxfee"], n) && n > 0)
            ::minRelayTxFee = CFeeRate(n);
        else
            return InitError(AmountErrMsg("minrelaytxfee", mapArgs["-minrelaytxfee"]));
    }
    fRequireStandard = !GetBoolArg("-acceptnonstdtxn", !Params().RequireStandard());
    if (Params().RequireStandard() && !fRequireStandard)
        return InitError(strprintf("acceptnonstdtxn is not currently supported for %s chain", chainparams.NetworkIDString()));
    nBytesPerSigOp = GetArg("-bytespersigop", nBytesPerSigOp);
#ifdef ENABLE_WALLET
    if (!CWallet::ParameterInteraction())
        return false;
#endif 
    fIsBareMultisigStd = GetBoolArg("-permitbaremultisig", DEFAULT_PERMIT_BAREMULTISIG);
    fAcceptDatacarrier = GetBoolArg("-datacarrier", DEFAULT_ACCEPT_DATACARRIER);
    nMaxDatacarrierBytes = GetArg("-datacarriersize", nMaxDatacarrierBytes);