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.

UpdateParent(updateIt, it, false);
    }
}
void CTxMemPool::UpdateForRemoveFromMempool(const setEntries &entriesToRemove, bool updateDescendants)
{
    
    
    const uint64_t nNoLimit = std::numeric_limits<uint64_t>::max();
    if (updateDescendants) {
        
        
        
        
        
        
        BOOST_FOREACH(txiter removeIt, entriesToRemove) {
            setEntries setDescendants;
            CalculateDescendants(removeIt, setDescendants);
            setDescendants.erase(removeIt); 
            int64_t modifySize = -((int64_t)removeIt->GetTxSize());
            CAmount modifyFee = -removeIt->GetModifiedFee();
            int modifySigOps = -removeIt->GetSigOpCost();
            BOOST_FOREACH(txiter dit, setDescendants) {
                mapTx.modify(dit, update_ancestor_state(modifySize, modifyFee, -1, modifySigOps));
            }
        }
    }
    BOOST_FOREACH(txiter removeIt, entriesToRemove) {