From time to time, the retailers will temporarily discount the price of your book. You will know that your price has been discounted when the original price is crossed out and a lesser price is displayed.
The reason the retailers will temporarily discount your price is to drive more traffic to your site and encourage more sales. Unfortunately we are unable to control when this happens and this can happen on any retail site.
The good news is that this discount does not impact your royalties and you will receive the same that you would at the original price.