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.

void FindFilesToPrune(std::set<int>& setFilesToPrune, uint64_t nPruneAfterHeight);
/**
 *  Actually unlink the specified files
 */
void UnlinkPrunedFiles(std::set<int>& setFilesToPrune);
CBlockIndex * InsertBlockIndex(uint256 hash);
bool GetNodeStateStats(NodeId nodeid, CNodeStateStats &stats);
void Misbehaving(NodeId nodeid, int howmuch);
void FlushStateToDisk();
void PruneAndFlush();
bool AcceptToMemoryPool(CTxMemPool& pool, CValidationState &state, const CTransaction &tx, bool fLimitFree,
                        bool* pfMissingInputs, bool fOverrideMempoolLimit=false, const CAmount nAbsurdFee=0);
std::string FormatStateMessage(const CValidationState &state);
ThresholdState VersionBitsTipState(const Consensus::Params& params, Consensus::DeploymentPos pos);
struct CNodeStateStats {
    int nMisbehavior;
    int nSyncHeight;
    int nCommonHeight;
    std::vector<int> vHeightInFlight;
};
/** 
 * Count ECDSA signature operations the old-fashioned (pre-0.6) way
 * @return number of sigops this transaction's outputs will produce when spent
 * @see CTransaction::FetchInputs
 */
unsigned int GetLegacySigOpCount(const CTransaction& tx);
/**
 * Count ECDSA signature operations in pay-to-script-hash inputs.
 * 
 * @param[in] mapInputs Map of previous transactions that have outputs we're spending