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 (!fHaveWitness) {
        for (size_t i = 0; i < block.vtx.size(); i++) {
            if (!block.vtx[i].wit.IsNull()) {
                return state.DoS(100, error("%s : unexpected witness data found", __func__), REJECT_INVALID, "unexpected-witness", true);
            }
        }
    }
    
    
    
    
    
    
    if (GetBlockWeight(block) > MAX_BLOCK_WEIGHT) {
        return state.DoS(100, error("ContextualCheckBlock(): weight limit failed"), REJECT_INVALID, "bad-blk-weight");
    }
    return true;
}
static bool AcceptBlockHeader(const CBlockHeader& block, CValidationState& state, const CChainParams& chainparams, CBlockIndex** ppindex=NULL)
{
    AssertLockHeld(cs_main);
    
    uint256 hash = block.GetHash();
    BlockMap::iterator miSelf = mapBlockIndex.find(hash);
    CBlockIndex *pindex = NULL;
    if (hash != chainparams.GetConsensus().hashGenesisBlock) {
        if (miSelf != mapBlockIndex.end()) {