I've read http://css3pie.com/documentation/known-issues and I didn't find the solution because my problem is another or I'm not understanding well some issue. My website is http://lad3.ia.uned.es, it's a drupal installation. I'm doing the testing with the next element:

article h2.node-title a {
display: block;
position: relative;
padding: 0.5em 1em;
color: #FFF;
margin-bottom: 0;
-webkit-border-radius: 10px 10px 0 0;
-moz-border-radius: 10px 10px 0 0;
-o-border-radius: 10px 10px 0 0;
border-radius: 10px 10px 0 0;
background: #93c5e4; /* Old browsers */
zoom:1;
behavior: url('/sites/all/libraries/PIE/PIE.htc');
}

You can see that the position is relative, the url path is abosolute from the domain root, I'm using the shorthand and I'm applying zoom:1. What could be? some conflict with js libraries?

I think that my webserver is well configured, too.

Thanks in advance!

You have script errors on your page; remove them and try again. If you clean up all the script errors and still have a problem, post again.