Why is Set Incompatible with Proxy?

JavaScript Set appears to be entirely incompatible with JavaScript proxies, attempting to Proxy() a Set()

var p = new Proxy(new Set(), {
  add(target, val, receiver) {
    console.log('in add: ', target, val, receiver)
  }
})
p.add(55)

results in a VMError:

Uncaught TypeError: Method Set.prototype.add called on incompatible receiver [object Object]
    at Proxy.add (native)
    at <anonymous>:1:3

In fact, proxying a Set() in any way breaks it categorically - even if our proxy handler does nothing at all! Compare p = new Proxy({}, {}) vs p = new Proxy(new Set(), {}). (This applies both in Firefox (52.0.2) and Chromium (57.0.2987.133).)

I can't seem to find a credible reference or documentation for this, why cannot JavaScript Proxy a Set object and why is it hitting a VM Error?