I have an e-commerce site and have noticed a strange phenomena. For my main keywords, my rankings remain fairly stable but the result that appears in the Google rankings frequently swaps between the homepage and the main category page. For many of my competitors, they will appear multiple times with multiple pages ranking for the same keyword. However, in my case, it is only one page or the other. Therefore, if it is the category page that is being displayed in the rankings, the homepage will completely disappear for the same term. Has anyone else experienced this? Is there any explanation for why this may occur?