Unexpected CSS3pie issue

I have shifted between using CSS3pie and not over the past year from http://css3pie.com. I really appreciate all the work that's gone into it. Sometimes it just doesn't work for me. This morning, I started to look at why it was not working on my portableCMS. I started to gradually remove elements and discovered that if I removed the colour from my body background ie from:
background:#FFFFFF url(images/bodyBackground.png) repeat-x;
to
background:url(images/bodyBackground.png) repeat-x;
I got partial site of my rounded corners etc.

Then I found this blog post. http://www.jakobloekkemadsen.com/2010/10/how-to-make-css3pie-work/
So I put, position:relative; in the CSS call to my selector which used PIE.htc and hey presto!