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.

LogPrintf("Peer %d sent us invalid header via cmpctblock\n", pfrom->id);
                return true;
            }
        }
        
        assert(pindex);
        UpdateBlockAvailability(pfrom->GetId(), pindex->GetBlockHash());
        std::map<uint256, pair<NodeId, list<QueuedBlock>::iterator> >::iterator blockInFlightIt = mapBlocksInFlight.find(pindex->GetBlockHash());
        bool fAlreadyInFlight = blockInFlightIt != mapBlocksInFlight.end();
        if (pindex->nStatus & BLOCK_HAVE_DATA) 
            return true;
        if (pindex->nChainWork <= chainActive.Tip()->nChainWork || 
                pindex->nTx != 0) { 
            if (fAlreadyInFlight) {
                
                
                std::vector<CInv> vInv(1);
                vInv[0] = CInv(MSG_BLOCK, cmpctblock.header.GetHash());
                pfrom->PushMessage(NetMsgType::GETDATA, vInv);
                return true;
            }
        }
        
        if (!fAlreadyInFlight && !CanDirectFetch(chainparams.GetConsensus()))
            return true;
        CNodeState *nodestate = State(pfrom->GetId());
        
        
        if (pindex->nHeight <= chainActive.Height() + 2) {
            if ((!fAlreadyInFlight && nodestate->nBlocksInFlight < MAX_BLOCKS_IN_TRANSIT_PER_PEER) ||