Some slides replace each other, order by date doesn’t work

I have a slider added with this shortcode: “[nivo post_type=”post” category=”12″ ribbon=”no” caption=”no” link=”no” theme=”oik” orderby=”date”]” on my page.
Some slides display instead of other ones. So, for example, if I reloaded the page the slide of Tracy appears, another time – John’ slide. I’ve tried to add one more slide and it displays correctly so the problem is not with the posts per page. The problem is with the strange and unpredictable substitution of one slide by other.
Also, slides are ordered by the date but this function doesn’t work too. The Tracy’s slide should be the last one (because this is the newest post) and instead, it goes the second one.

The page I need help with: [log in to see the link]