a uint storage variable can't be reset to 0

when test a contract i meet a confusing condition, so i tracked it by commented out per line, and distinguish it’s a uint storage variable be reset to 0. To make it clear, i write a test contract like below, and it reappear this error.

pragma solidity ^0.4.18;

contract testReset {

    uint public _num;

    constructor() public {
    }


    function _set(uint newnum) public {
        _num = newnum;
    }

    function _reset() public {
        _num = 0;
    }
}

1) set to any number like 20;
2) reset to 0, but remix report error: “base fee exceeds gas limit.”

my environment is remix + ganache-cli, and compiler version is 0.4.24.

is it a solidity’s bug?