    fallback(bytes calldata _data) external onlySystemCall returns (bytes memory)
    modifier onlySystemCall() {
        require(
            SystemContractHelper.isSystemCall() || SystemContractHelper.isSystemContract(msg.sender),
                "This method require system call flag"
        );
        _;
    }
            _loadFarCallABIIntoActivePtr(_gas, _data, false, true); <========= isSystem hard-coded to true

            // If there is provided `msg.value` call the `MsgValueSimulator` to forward ether.
            address msgValueSimulator = MSG_VALUE_SYSTEM_CONTRACT;
            address callAddr = SYSTEM_CALL_BY_REF_CALL_ADDRESS;
            // We need to supply the mask to the MsgValueSimulator to denote
            // that the call should be a system one.
            uint256 forwardMask = _isSystem ? MSG_VALUE_SIMULATOR_IS_SYSTEM_BIT : 0; <========= may be false
    function rawCall(
        uint256 _gas,
        address _address,
        uint256 _value,
        bytes calldata _data,
        bool _isSystem
    ) internal returns (bool success) {
        if (_value == 0) {
            _loadFarCallABIIntoActivePtr(_gas, _data, false, _isSystem);

            address callAddr = RAW_FAR_CALL_BY_REF_CALL_ADDRESS;
            assembly {
                success := call(_address, callAddr, 0, 0, 0xFFFF, 0, 0)
            }
        } else {
            _loadFarCallABIIntoActivePtr(_gas, _data, false, true);

            // If there is provided `msg.value` call the `MsgValueSimulator` to forward ether.
            address msgValueSimulator = MSG_VALUE_SYSTEM_CONTRACT;
            address callAddr = SYSTEM_CALL_BY_REF_CALL_ADDRESS;
-           // We need to supply the mask to the MsgValueSimulator to denote
-           // that the call should be a system one.
-           uint256 forwardMask = _isSystem ? MSG_VALUE_SIMULATOR_IS_SYSTEM_BIT : 0;
+           uint256 forwardMask = MSG_VALUE_SIMULATOR_IS_SYSTEM_BIT; 

            assembly {
                success := call(msgValueSimulator, callAddr, _value, _address, 0xFFFF, forwardMask, 0)
            }
        }
    }
