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.

{
    setEntries parentHashes;
    const CTransaction &tx = entry.GetTx();
    if (fSearchForParents) {
        
        
        
        for (unsigned int i = 0; i < tx.vin.size(); i++) {
            txiter piter = mapTx.find(tx.vin[i].prevout.hash);
            if (piter != mapTx.end()) {
                parentHashes.insert(piter);
                if (parentHashes.size() + 1 > limitAncestorCount) {
                    errString = strprintf("too many unconfirmed parents [limit: %u]", limitAncestorCount);
                    return false;
                }
            }
        }
    } else {
        
        
        txiter it = mapTx.iterator_to(entry);
        parentHashes = GetMemPoolParents(it);
    }
    size_t totalSizeWithAncestors = entry.GetTxSize();