The keymap defaultTabBinding doesn't work

I keep trying to get tabs to focus on the CodeMirror 6 Editor but it keeps shifting to other focusable elements, even after following the instructions CodeMirror Tab Handling Example. Here is a link to a demo displaying what I mean:

Interesting. I can see the issue in the codepen, but I can’t reproduce it locally with the same code. Keymaps in general don’t seem to work on that codepen (but do work for everybody else). If I simplify the code in the codepen to this, it works again:

import { keymap , EditorView } from "";
import { EditorState } from "";
import { defaultTabBinding, defaultKeymap } from "";
let editor = new EditorView({
    state: EditorState.create({
        doc: "abc",
        extensions: [
            keymap.of([...defaultKeymap, defaultTabBinding]),

    parent: document.querySelector("#editor")

I think skypack is messing something up by duplicating dependencies, and that’s where the problem originates.