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(cs);
    unsigned nTxnRemoved = 0;
    CFeeRate maxFeeRateRemoved(0);
    while (!mapTx.empty() && DynamicMemoryUsage() > sizelimit) {
        indexed_transaction_set::index<descendant_score>::type::iterator it = mapTx.get<descendant_score>().begin();
        
        
        
        
        CFeeRate removed(it->GetModFeesWithDescendants(), it->GetSizeWithDescendants());
        removed += minReasonableRelayFee;
        trackPackageRemoved(removed);
        maxFeeRateRemoved = std::max(maxFeeRateRemoved, removed);
        setEntries stage;
        CalculateDescendants(mapTx.project<0>(it), stage);
        nTxnRemoved += stage.size();
        std::vector<CTransaction> txn;
        if (pvNoSpendsRemaining) {
            txn.reserve(stage.size());
            BOOST_FOREACH(txiter it, stage)
                txn.push_back(it->GetTx());
        }
        RemoveStaged(stage, false);
        if (pvNoSpendsRemaining) {
            BOOST_FOREACH(const CTransaction& tx, txn) {