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.

CheckBlockIndex(chainparams.GetConsensus());
    }
    else if (strCommand == NetMsgType::BLOCKTXN && !fImporting && !fReindex) 
    {
        BlockTransactions resp;
        vRecv >> resp;
        LOCK(cs_main);
        map<uint256, pair<NodeId, list<QueuedBlock>::iterator> >::iterator it = mapBlocksInFlight.find(resp.blockhash);
        if (it == mapBlocksInFlight.end() || !it->second.second->partialBlock ||
                it->second.first != pfrom->GetId()) {
            LogPrint("net", "Peer %d sent us block transactions for block we weren't expecting\n", pfrom->id);
            return true;
        }
        PartiallyDownloadedBlock& partialBlock = *it->second.second->partialBlock;
        CBlock block;
        ReadStatus status = partialBlock.FillBlock(block, resp.txn);
        if (status == READ_STATUS_INVALID) {
            MarkBlockAsReceived(resp.blockhash); 
            Misbehaving(pfrom->GetId(), 100);
            LogPrintf("Peer %d sent us invalid compact block/non-matching block transactions\n", pfrom->id);
            return true;
        } else if (status == READ_STATUS_FAILED) {
            
            std::vector<CInv> invs;
            invs.push_back(CInv(MSG_BLOCK, resp.blockhash));
            pfrom->PushMessage(NetMsgType::GETDATA, invs);
        } else {
            CValidationState state;
            ProcessNewBlock(state, chainparams, pfrom, &block, false, NULL);
            int nDoS;