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.

CService addrBind;
                if (!Lookup(strBind.c_str(), addrBind, GetListenPort(), false))
                    return InitError(ResolveErrMsg("bind", strBind));
                fBound |= Bind(addrBind, (BF_EXPLICIT | BF_REPORT_ERROR));
            }
            BOOST_FOREACH(const std::string& strBind, mapMultiArgs["-whitebind"]) {
                CService addrBind;
                if (!Lookup(strBind.c_str(), addrBind, 0, false))
                    return InitError(ResolveErrMsg("whitebind", strBind));
                if (addrBind.GetPort() == 0)
                    return InitError(strprintf(_("Need to specify a port with -whitebind: '%s'"), strBind));
                fBound |= Bind(addrBind, (BF_EXPLICIT | BF_REPORT_ERROR | BF_WHITELIST));
            }
        }
        else {
            struct in_addr inaddr_any;
            inaddr_any.s_addr = INADDR_ANY;
            fBound |= Bind(CService(in6addr_any, GetListenPort()), BF_NONE);
            fBound |= Bind(CService(inaddr_any, GetListenPort()), !fBound ? BF_REPORT_ERROR : BF_NONE);
        }
        if (!fBound)
            return InitError(_("Failed to listen on any port. Use -listen=0 if you want this."));
    }
    if (mapArgs.count("-externalip")) {
        BOOST_FOREACH(const std::string& strAddr, mapMultiArgs["-externalip"]) {