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.

nTransactionsUpdated(0)
{
    _clear(); 
    
    
    
    nCheckFrequency = 0;
    minerPolicyEstimator = new CBlockPolicyEstimator(_minReasonableRelayFee);
    minReasonableRelayFee = _minReasonableRelayFee;
}
CTxMemPool::~CTxMemPool()
{
    delete minerPolicyEstimator;
}
void CTxMemPool::pruneSpent(const uint256 &hashTx, CCoins &coins)
{
    LOCK(cs);
    auto it = mapNextTx.lower_bound(COutPoint(hashTx, 0));
    
    while (it != mapNextTx.end() && it->first->hash == hashTx) {
        coins.Spend(it->first->n); 
        it++;
    }
}
unsigned int CTxMemPool::GetTransactionsUpdated() const