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.

}
                LOCK(pto->cs_filter);
                for (const auto& txinfo : vtxinfo) {
                    const uint256& hash = txinfo.tx->GetHash();
                    CInv inv(MSG_TX, hash);
                    pto->setInventoryTxToSend.erase(hash);
                    if (filterrate) {
                        if (txinfo.feeRate.GetFeePerK() < filterrate)
                            continue;
                    }
                    if (pto->pfilter) {
                        if (!pto->pfilter->IsRelevantAndUpdate(*txinfo.tx)) continue;
                    }
                    pto->filterInventoryKnown.insert(hash);
                    vInv.push_back(inv);
                    if (vInv.size() == MAX_INV_SZ) {
                        pto->PushMessage(NetMsgType::INV, vInv);
                        vInv.clear();
                    }
                }
                pto->timeLastMempoolReq = GetTime();
            }
            
            if (fSendTrickle) {
                
                vector<std::set<uint256>::iterator> vInvTx;
                vInvTx.reserve(pto->setInventoryTxToSend.size());
                for (std::set<uint256>::iterator it = pto->setInventoryTxToSend.begin(); it != pto->setInventoryTxToSend.end(); it++) {
                    vInvTx.push_back(it);
                }