yeah.. thumbs etc. are a freakin pain in the ass for hovers etc. Maybe try this.. Note you need to set the width and height.
Code:
a.blah:link,a.blah:hover,a.blah:active{
width:XXpx;
height:XXpx;
border:1px solid #00f;
text-decoration:none;
padding:4px;
display:block;
}
a.blah:hover{
border:1px solid #f00;
}