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.

typedef std::map<uint256, std::shared_ptr<const CTransaction>> MapRelay;
    MapRelay mapRelay;
    
    std::deque<std::pair<int64_t, MapRelay::iterator>> vRelayExpiration;
} 
namespace {
struct CBlockReject {
    unsigned char chRejectCode;
    string strRejectReason;
    uint256 hashBlock;
};
/**
 * Maintain validation-specific state about nodes, protected by cs_main, instead
 * by CNode's own locks. This simplifies asynchronous operation, where
 * processing of incoming data is done after the ProcessMessage call returns,
 * and we're no longer holding the node's locks.
 */
struct CNodeState {
    
    CService address;
    
    bool fCurrentlyConnected;
    
    int nMisbehavior;
    
    bool fShouldBan;
    
    std::string name;
    
    std::vector<CBlockReject> rejects;