Hi. I'm the developer of the plugin.
What you are experiencing is not a bug in the plugin, that's just how it works. I guess I need to document that better to avoid confusion.
The plugin intended for changing the post order, not the post date.
You would typically use a plugin like this in conjunction with a custom post-type. The core code of this was originally built to handle the reordering of e-commerce products within a custom e-commerce plugin. I abstracted that out into the plugin you downloaded so that it could be reused on multiple sites. It was never designed with reordering by date in mind, although it looks like mhamann has kindly found a solution to achieve that for anyone who feels that would be useful.