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.

cachedInnerUsage += entry.DynamicMemoryUsage();
    const CTransaction& tx = newit->GetTx();
    std::set<uint256> setParentTransactions;
    for (unsigned int i = 0; i < tx.vin.size(); i++) {
        mapNextTx.insert(std::make_pair(&tx.vin[i].prevout, &tx));
        setParentTransactions.insert(tx.vin[i].prevout.hash);
    }
    
    
    
    
    
    
    
    BOOST_FOREACH (const uint256 &phash, setParentTransactions) {
        txiter pit = mapTx.find(phash);
        if (pit != mapTx.end()) {
            UpdateParent(newit, pit, true);
        }
    }
    UpdateAncestorsOf(true, newit, setAncestors);
    UpdateEntryForAncestors(newit, setAncestors);
    nTransactionsUpdated++;
    totalTxSize += entry.GetTxSize();
    minerPolicyEstimator->processTransaction(entry, fCurrentEstimate);
    vTxHashes.emplace_back(hash, newit);
    newit->vTxHashesIdx = vTxHashes.size() - 1;
    return true;
}
void CTxMemPool::removeUnchecked(txiter it)