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.

InitWarning(strprintf(_("Reducing -maxconnections from %d to %d, because of system limitations."), nUserMaxConnections, nMaxConnections));
    
    fDebug = !mapMultiArgs["-debug"].empty();
    
    const vector<string>& categories = mapMultiArgs["-debug"];
    if (GetBoolArg("-nodebug", false) || find(categories.begin(), categories.end(), string("0")) != categories.end())
        fDebug = false;
    
    if (GetBoolArg("-debugnet", false))
        InitWarning(_("Unsupported argument -debugnet ignored, use -debug=net."));
    
    if (mapArgs.count("-socks"))
        return InitError(_("Unsupported argument -socks found. Setting SOCKS version isn't possible anymore, only SOCKS5 proxies are supported."));
    
    if (GetBoolArg("-tor", false))
        return InitError(_("Unsupported argument -tor found, use -onion."));
    if (GetBoolArg("-benchmark", false))
        InitWarning(_("Unsupported argument -benchmark ignored, use -debug=bench."));
    if (GetBoolArg("-whitelistalwaysrelay", false))
        InitWarning(_("Unsupported argument -whitelistalwaysrelay ignored, use -whitelistrelay and/or -whitelistforcerelay."));
    if (mapArgs.count("-blockminsize"))
        InitWarning("Unsupported argument -blockminsize ignored.");
    
    int ratio = std::min<int>(std::max<int>(GetArg("-checkmempool", chainparams.DefaultConsistencyChecks() ? 1 : 0), 0), 1000000);
    if (ratio != 0) {
        mempool.setSanityCheck(1.0 / ratio);
    }
    fCheckBlockIndex = GetBoolArg("-checkblockindex", chainparams.DefaultConsistencyChecks());
    fCheckpointsEnabled = GetBoolArg("-checkpoints", DEFAULT_CHECKPOINTS_ENABLED);