Parcel breaks XMLHttpRequest

Question

var xhttp = new XMLHttpRequest();
xhttp.onreadystatechange = function() {
    if (this.readyState == 4 && this.status == 200) {
       document.getElementById("demo").innerHTML = xhttp.responseText;
    }
};
xhttp.open("GET", "/html/other_page.html", true);
xhttp.send();

Without Parcel: XMLHttpRequest returns /html/other_page.html

With Parcel: XMLHttpRequest returns index.html

With Parcel caching on, I get a 304 redirect. With Parcel caching off, I get a 200 response. Either way, the XMLHttpRequest sends me to index.html instead of /html/other_page.html.

Anyone know what's going on with Parcel? It's gotta be related to the minified js or the cache, but I can't make heads or tales of what Parcel is doing behind the scenes.