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.

(fAlreadyInFlight && blockInFlightIt->second.first == pfrom->GetId())) {
                list<QueuedBlock>::iterator *queuedBlockIt = NULL;
                if (!MarkBlockAsInFlight(pfrom->GetId(), pindex->GetBlockHash(), chainparams.GetConsensus(), pindex, &queuedBlockIt)) {
                    if (!(*queuedBlockIt)->partialBlock)
                        (*queuedBlockIt)->partialBlock.reset(new PartiallyDownloadedBlock(&mempool));
                    else {
                        
                        LogPrint("net", "Peer sent us compact block we were already syncing!\n");
                        return true;
                    }
                }
                PartiallyDownloadedBlock& partialBlock = *(*queuedBlockIt)->partialBlock;
                ReadStatus status = partialBlock.InitData(cmpctblock);
                if (status == READ_STATUS_INVALID) {
                    MarkBlockAsReceived(pindex->GetBlockHash()); 
                    Misbehaving(pfrom->GetId(), 100);
                    LogPrintf("Peer %d sent us invalid compact block\n", pfrom->id);
                    return true;
                } else if (status == READ_STATUS_FAILED) {
                    
                    std::vector<CInv> vInv(1);
                    vInv[0] = CInv(MSG_BLOCK, cmpctblock.header.GetHash());
                    pfrom->PushMessage(NetMsgType::GETDATA, vInv);
                    return true;
                }
                BlockTransactionsRequest req;
                for (size_t i = 0; i < cmpctblock.BlockTxCount(); i++) {
                    if (!partialBlock.IsTxAvailable(i))
                        req.indexes.push_back(i);
                }