Find in your CSS (on line 915 of style.css for the Twenty Ten theme):
#nav-below {
margin: -18px 0 0 0;
}
change to:
#nav-below {
margin: 10px 0;
}
What’s happening is that the #nav-below is getting pushed up into your other content due to the minus. It’s not a glitch either or relevant to WordPress itself, someone just made some mistakes when styling the CSS.