Works for me as well, but I believe it is only intended to be used with the trash folder. It is not meant to 'Empty' a folder other than the Trash.
And while we are talking about this, I tweaked the Javascript file on my install so the confirm dialog box is not displayed and my trash is just emptied when I click "Empty." This was not a hard tweak if you are interested in making this change, this might be something that could be added to the config/main.inc.php as a TRUE/FALSE variable in future releases.
For now, just comment out two lines in the program/js/app.js file. Those two lines are shown below with my comment above them.
// commented this out so the confirm delete dialog is not displayed
//if (!confirm(this.get_label('purgefolderconfirm')))
//return false;