Available Plugins list reports that list "has not been downloaded" when all available plugins are installed

It appears this is caused by the fact that I had downloaded and installed all of the plugins by downloading them from the web and saving them into the plugin directory, so there were no available-but-uninstalled plugins. If you remove a plug-in, the page shows as expected. If you re-install that plug-in, then it goes back to the "has not yet been downloaded" behavior.