I don’t know if it will help in this instance as I haven’t tried installing the 2 or 3 things I’ve purchased since the new store opened, but on other sites where I’ve had problems when left-clicking on download links, I instead right-click and choose “Save As” to download, and then everything is fine.
Again, I’m not sure if it will worth with the new store downloads because of the known installer issues, but I think it might be worth a try.