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.

{
    CBlockIndex *pindexDelete = chainActive.Tip();
    assert(pindexDelete);
    
    CBlock block;
    if (!ReadBlockFromDisk(block, pindexDelete, chainparams.GetConsensus()))
        return AbortNode(state, "Failed to read block");
    
    int64_t nStart = GetTimeMicros();
    {
        CCoinsViewCache view(pcoinsTip);
        if (!DisconnectBlock(block, state, pindexDelete, view))
            return error("DisconnectTip(): DisconnectBlock %s failed", pindexDelete->GetBlockHash().ToString());
        assert(view.Flush());
    }
    LogPrint("bench", "- Disconnect block: %.2fms\n", (GetTimeMicros() - nStart) * 0.001);
    
    if (!FlushStateToDisk(state, FLUSH_STATE_IF_NEEDED))
        return false;
    if (!fBare) {
        
        std::vector<uint256> vHashUpdate;
        BOOST_FOREACH(const CTransaction &tx, block.vtx) {