AsyncMirror with IndexDB does not seem to sync

[vrthra]

I am trying to use BrowserFS with pyodide. My configuration is as follows

BrowserFS.configure({
  fs: "AsyncMirror",
  options: {
    sync: { fs: "InMemory" },
    async: {
      fs: "IndexedDB",
      options: { storeName: "pythoninstall", },
    }
    // cacheSize: 100 MB is default inode cache.
  }
}, function(e) {
if (e) { throw e; }
languagePluginLoader.then(() => {
  // https://github.com/pyodide/pyodide/issues/613
  let FS = pyodide._module.FS;
  let PATH = pyodide._module.PATH;
  // Create an Emscripten interface for the BrowserFS
  var BFS = new BrowserFS.EmscriptenFS(FS, PATH);
  // Create mount point in Emscripten FS
  //FS.createFolder(FS.root, 'data', true, true);
  FS.createPath(FS.root, 'data', true, true);
  // Mount BrowserFS into Emscripten FS
  FS.mount(BFS, {root: '/'}, '/data');
...
})

Next, within pyodide, I try this in one window.

with open('/data/x.txt', 'w+') as f:
     f.write('Hi there\n')

This works in the same window

with open('/data/verify.txt') as f:
     print(f.read())

But not if I use a different window.

According to the AsyncMirror docs, both backends should be kept in sync. However, the write operation does not seem to be synced to IndexDB even after some time has passed.