I had a similar problem after uploading a new interior file. I forgot all about the checkbox at the bottom of the second "Rights and Pricing" tab. Click that on 2nd tab, THEN click button to proceed/publish. Maybe the same thing applies to your problem.
You have to go through the complete publishing process to change the description, so after changing the blurb, you have to go to the pricing page and click save and publish. You don't have to re-upload the book, though.