"Mime" icons not showing in FF, sporadic in IE

Hello all

I have this CSS which applies little "mime" icons to PDF and Word links:

a.pdf:link {
color:#058; 
background-image:url(../images/pdf.gif); 
background-repeat:no-repeat; 
background-position:center left; 
padding-left:18px
}

and obviously I apply the class to links with class="pdf". However, it doesn't work on all links in FF and some in IE. There appeared to be a bug where it wouldn't work when the link was wrapped between two lines, which I can live with, but in many cases it is now not showing at all.

You can see what I mean here:

http://www.scotlawcom.gov.uk

(see the news panel on the right - the links near the top don't have the icons while the ones near the bottom do. You can see if you hover which ones should have them - i.e. the PDFs.)

Elsewhere in the site they seem to work fine, but I can't understand what is going wrong here, since they should presumably always work or not work at all.

Any help would be much appreciated