That happens when the style sheet for a particular site or page is not loading correctly. The style sheet tells your browser how to display the page so that you do not need to reload every bit of information about the page each time you go to that page, which can make things load much faster, if it works as it should.
You can bypass your cached copy of the page by holding down the shift key and refreshing the page in most PC browsers. If that does not help, try manually erasing just your eBay cookies.
As to why it seems to happen for you so often, that might be a sign that your browser is not saving cookies properly, or not allowing cookies to be updated as they should. It can also happen when using an older version of a browser.
Try another browser and see if the same problem recurs. If the same problem keeps happening, that might be a sign of something else causing a problem, or of a network issue.
