Using object as key of object makes strange behavior

[vadjs]

o = {};
k = {a: 1, b: 2};
o[k] = 1;
console.log(o[k]);    //1
console.log({a: 1, b: 2});  //1
k.a = 5;
console.log(o[k]);    //1
console.log({a: 1, b: 2});  //1
o[{a: 1, b: 2}] = 2
console.log(o[k]);    //2
console.log({a: 1, b: 2});  //2

Is it ECMAScript bug? Or it's "very specific" explainable mechanics?

[ljharb]

Object keys can only be strings or symbols; if you do Object.keys(o) you’ll see that the object has been turned into the string ’[object Object]’.

[ljharb]

Object keys can only be strings or symbols; if you do Object.keys(o) you’ll see that the object has been turned into the string ’[object Object]’.