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.

map<uint256, pair<NodeId, list<QueuedBlock>::iterator> >::iterator itInFlight = mapBlocksInFlight.find(hash);
    if (itInFlight != mapBlocksInFlight.end()) {
        CNodeState *state = State(itInFlight->second.first);
        state->nBlocksInFlightValidHeaders -= itInFlight->second.second->fValidatedHeaders;
        if (state->nBlocksInFlightValidHeaders == 0 && itInFlight->second.second->fValidatedHeaders) {
            
            nPeersWithValidatedDownloads--;
        }
        if (state->vBlocksInFlight.begin() == itInFlight->second.second) {
            
            state->nDownloadingSince = std::max(state->nDownloadingSince, GetTimeMicros());
        }
        state->vBlocksInFlight.erase(itInFlight->second.second);
        state->nBlocksInFlight--;
        state->nStallingSince = 0;
        mapBlocksInFlight.erase(itInFlight);
        return true;
    }
    return false;
}
bool MarkBlockAsInFlight(NodeId nodeid, const uint256& hash, const Consensus::Params& consensusParams, CBlockIndex *pindex = NULL, list<QueuedBlock>::iterator **pit = NULL) {