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.

sigemptyset(&sa_hup.sa_mask);
    sa_hup.sa_flags = 0;
    sigaction(SIGHUP, &sa_hup, NULL);
    
    signal(SIGPIPE, SIG_IGN);
#endif
    
    const CChainParams& chainparams = Params();
    
    
    if (GetArg("-prune", 0)) {
        if (GetBoolArg("-txindex", DEFAULT_TXINDEX))
            return InitError(_("Prune mode is incompatible with -txindex."));
#ifdef ENABLE_WALLET
        if (GetBoolArg("-rescan", false)) {
            return InitError(_("Rescans are not possible in pruned mode. You will need to use -reindex which will download the whole blockchain again."));
        }
#endif
    }
    
    int nBind = std::max((int)mapArgs.count("-bind") + (int)mapArgs.count("-whitebind"), 1);
    int nUserMaxConnections = GetArg("-maxconnections", DEFAULT_MAX_PEER_CONNECTIONS);
    nMaxConnections = std::max(nUserMaxConnections, 0);
    
    nMaxConnections = std::max(std::min(nMaxConnections, (int)(FD_SETSIZE - nBind - MIN_CORE_FILEDESCRIPTORS)), 0);
    int nFD = RaiseFileDescriptorLimit(nMaxConnections + MIN_CORE_FILEDESCRIPTORS);
    if (nFD < MIN_CORE_FILEDESCRIPTORS)
        return InitError(_("Not enough file descriptors available."));
    nMaxConnections = std::min(nFD - MIN_CORE_FILEDESCRIPTORS, nMaxConnections);
    if (nMaxConnections < nUserMaxConnections)