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.

{
    {
        LOCK(cs_main);
        bool fRequested = MarkBlockAsReceived(pblock->GetHash());
        fRequested |= fForceProcessing;
        
        CBlockIndex *pindex = NULL;
        bool fNewBlock = false;
        bool ret = AcceptBlock(*pblock, state, chainparams, &pindex, fRequested, dbp, &fNewBlock);
        if (pindex && pfrom) {
            mapBlockSource[pindex->GetBlockHash()] = pfrom->GetId();
            if (fNewBlock) pfrom->nLastBlockTime = GetTime();
        }
        CheckBlockIndex(chainparams.GetConsensus());
        if (!ret)
            return error("%s: AcceptBlock FAILED", __func__);
    }
    NotifyHeaderTip();
    if (!ActivateBestChain(state, chainparams, pblock))
        return error("%s: ActivateBestChain failed", __func__);
    return true;
}
bool TestBlockValidity(CValidationState& state, const CChainParams& chainparams, const CBlock& block, CBlockIndex* pindexPrev, bool fCheckPOW, bool fCheckMerkleRoot)