For some readers who use Internet Explorer, the existence of a "Post Reply" button on comments must have seemed rather confusing, as it didn't do anything when clicked, and replies had to be entered using the box below all the other comments. From the best we can tell, this issue cropped up when IE8 was released, so it's been around for a very long time (as Internet time goes).
Now it has been fixed.
Below is a screen capture of what you should see now when you click "Post Reply" to a specific comment.
Internet Explorer (9.0)
Select Tools from the top menu.
Choose Internet Options.
Click on the Security tab.
Click on Custom Level.
Scroll down until you see the section labeled 'Scripting.'
Under 'Active Scripting,' select Enable and click OK.