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.

if (height != tip->nHeight+1) {
                    maxInputHeight = std::max(maxInputHeight, height);
                }
            }
            lp->maxInputBlock = tip->GetAncestor(maxInputHeight);
        }
    }
    return EvaluateSequenceLocks(index, lockPair);
}
unsigned int GetLegacySigOpCount(const CTransaction& tx)
{
    unsigned int nSigOps = 0;
    BOOST_FOREACH(const CTxIn& txin, tx.vin)
    {
        nSigOps += txin.scriptSig.GetSigOpCount(false);
    }
    BOOST_FOREACH(const CTxOut& txout, tx.vout)
    {
        nSigOps += txout.scriptPubKey.GetSigOpCount(false);
    }
    return nSigOps;
}
unsigned int GetP2SHSigOpCount(const CTransaction& tx, const CCoinsViewCache& inputs)