--- ./app/code/core/Mage/Catalog/Block/Navigation.php	2011-03-10 23:23:49.000000000 +0100
+++ ./app/code/local/Mage/Catalog/Block/Navigation.php	2011-03-11 11:12:45.000000000 +0100
@@ -193,7 +193,7 @@
         }
         $hasChildren = $children && $childrenCount;
         $html.= '<li';
-        if ($hasChildren) {
+        if ($hasChildren && $level == -1) {
              $html.= ' onmouseover="toggleMenu(this,1)" onmouseout="toggleMenu(this,0)"';
         }
 
@@ -206,7 +206,7 @@
         if ($last) {
             $html .= ' last';
         }
-        if ($hasChildren) {
+        if ($hasChildren && $level == -1) {
             $cnt = 0;
             foreach ($children as $child) {
                 if ($child->getIsActive()) {
@@ -220,7 +220,7 @@
         $html.= '">'."\n";
         $html.= '<a href="'.$this->getCategoryUrl($category).'"><span>'.$this->htmlEscape($category->getName()).'</span></a>'."\n";
 
-        if ($hasChildren){
+        if ($hasChildren && $level == -1) {
 
             $j = 0;
             $htmlChildren = '';