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.

while (!parentHashes.empty()) {
        txiter stageit = *parentHashes.begin();
        setAncestors.insert(stageit);
        parentHashes.erase(stageit);
        totalSizeWithAncestors += stageit->GetTxSize();
        if (stageit->GetSizeWithDescendants() + entry.GetTxSize() > limitDescendantSize) {
            errString = strprintf("exceeds descendant size limit for tx %s [limit: %u]", stageit->GetTx().GetHash().ToString(), limitDescendantSize);
            return false;
        } else if (stageit->GetCountWithDescendants() + 1 > limitDescendantCount) {
            errString = strprintf("too many descendants for tx %s [limit: %u]", stageit->GetTx().GetHash().ToString(), limitDescendantCount);
            return false;
        } else if (totalSizeWithAncestors > limitAncestorSize) {
            errString = strprintf("exceeds ancestor size limit [limit: %u]", limitAncestorSize);
            return false;
        }
        const setEntries & setMemPoolParents = GetMemPoolParents(stageit);
        BOOST_FOREACH(const txiter &phash, setMemPoolParents) {
            
            if (setAncestors.count(phash) == 0) {
                parentHashes.insert(phash);
            }
            if (parentHashes.size() + setAncestors.size() + 1 > limitAncestorCount) {
                errString = strprintf("too many unconfirmed ancestors [limit: %u]", limitAncestorCount);
                return false;
            }
        }
    }
    return true;
}
void CTxMemPool::UpdateAncestorsOf(bool add, txiter it, setEntries &setAncestors)