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.

FormatStateMessage(state));
            if (state.GetRejectCode() < REJECT_INTERNAL) 
                pfrom->PushMessage(NetMsgType::REJECT, strCommand, (unsigned char)state.GetRejectCode(),
                                   state.GetRejectReason().substr(0, MAX_REJECT_MESSAGE_LENGTH), inv.hash);
            if (nDoS > 0 && (!state.CorruptionPossible() || State(pfrom->id)->fHaveWitness)) {
                
                
                Misbehaving(pfrom->GetId(), nDoS);
            }
        }
        FlushStateToDisk(state, FLUSH_STATE_PERIODIC);
    }
    else if (strCommand == NetMsgType::CMPCTBLOCK && !fImporting && !fReindex) 
    {
        CBlockHeaderAndShortTxIDs cmpctblock;
        vRecv >> cmpctblock;
        LOCK(cs_main);
        if (mapBlockIndex.find(cmpctblock.header.hashPrevBlock) == mapBlockIndex.end()) {
            
            if (!IsInitialBlockDownload())
                pfrom->PushMessage(NetMsgType::GETHEADERS, chainActive.GetLocator(pindexBestHeader), uint256());
            return true;
        }
        CBlockIndex *pindex = NULL;
        CValidationState state;
        if (!AcceptBlockHeader(cmpctblock.header, state, chainparams, &pindex)) {
            int nDoS;
            if (state.IsInvalid(nDoS)) {
                if (nDoS > 0)
                    Misbehaving(pfrom->GetId(), nDoS);