I found a work-around until an update fixes this.
Instead of using the extension menu, right click on empty space on the web page playing the video you want to download. Select "Video DownloadHelper" near the bottom of the context menu, then click on the video stream you want to download.
You can't see download progress from here, but it does work.
If you don't see this option in the right-click menu, make sure the "Context Menu" option is checked under the "Appearance" tab in Video DownloadHelper extension settings.