That's happening when there isn't enough space for the text to fit on one line. Either the browser window is too small or the text is displayed too big. Since the grey graphic is a fixed size, you'll have to shrink the text to make it fit better.
To make the text smaller edit style.css in your theme and change:
.post-info{
background:transparent url(images/info-bar.png) no-repeat right top;
height:42px;
margin-left:11px;
font-style:italic;
color:#bbb;
}
to
.post-info{
background:transparent url(images/info-bar.png) no-repeat right top;
height:42px;
margin-left:11px;
font-style:italic;
color:#bbb;
font-size: 12px;
}
That will give the text more space and help it fit on one line over the grey graphic.