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.

{
    if (howmuch == 0)
        return;
    CNodeState *state = State(pnode);
    if (state == NULL)
        return;
    state->nMisbehavior += howmuch;
    int banscore = GetArg("-banscore", DEFAULT_BANSCORE_THRESHOLD);
    if (state->nMisbehavior >= banscore && state->nMisbehavior - howmuch < banscore)
    {
        LogPrintf("%s: %s (%d -> %d) BAN THRESHOLD EXCEEDED\n", __func__, state->name, state->nMisbehavior-howmuch, state->nMisbehavior);
        state->fShouldBan = true;
    } else
        LogPrintf("%s: %s (%d -> %d)\n", __func__, state->name, state->nMisbehavior-howmuch, state->nMisbehavior);
}
void static InvalidChainFound(CBlockIndex* pindexNew)