You probably just need to refresh the page.

After you've saved something, and you close the item box using the X in the top-right corner, you see the page you were on before, but it is still showing the old page. You need to refresh that page to see the new item.

You can do that in your browser (with the refresh button,  which in Firefox is that curly arrow next to the star

or you can just click the same menu item as before to re-load the page with the new item on it.