What's generating this weirdness?

Can anyone figure-out what's causing the weird rollover effect on my category menu at http://www.kentmusictechnology.co.uk/catalog - it's like an unwanted lilac background has been applied to the hover class.
It's only happening on IE, and I can't see anything in the style sheet that could be generating it.
Any ideas?

Im not going to speculate the exact cause, as IE is notorious for not parsing CSS correctly. That being said, adding a white background-color attribute to one (or more) of the following should fix it (background-color:#fff;)

/* categories box parent and child categories and extra links */
.category-top, .category-links {
display: block;
color: #333333;
text-decoration: none;
font-weight: bold;
margin: 0px 0px -7px 0px;
border-bottom: 0px solid #00639A;
}

.category-top a, .category-links a {
display: block;
color: #333333;
text-decoration: none;
font-weight: bold;
margin: 0px 0px -7px 0px;
border-bottom: 0px solid #00639A;
}

.category-top a:hover, .category-links a:hover {
color: #330066;
text-decoration: underline;
font-weight: bold;
}

Thanks. That did the trick - sort of. As well as making the background colour white I also had to set the width of .category-top, .category-links to 100%