Ah... that fact that your form is at the bottom of a page and requires an #anchor tag would have been an important thing to mention up front ;-)
It's not an issue with the plugin -- all it does it submit data to the current URL -- which the browser is responsible for setting. Using PHP_SELF or REQUEST_URI has security implications:
IE stripping the #hash from that... well that's IE's issue ;-(
In the end, insuring the form/success message is visible post submit is really a function of your theme -- any workaround I would add to preserve the #anchor in IE may cause other issues or add security issues for all users of the plugin. So, while that may happen if others report the same issue, it's low on the list of things to fix as it requires a workaround and reduces security overall.
My suggestion in your case would be to use a bit of jQuery to explicitly set the form action to include the needed #hash tag (using the workaround mentioned in the stack exchange article).