An update to the above: It appears that analogous menus display normally in IE8 in vanilla twentyeleven, so it is probably something that I’ve done in the child theme that is causing the problem. Here is the relevant css from the child:
#access div {
margin: 0 0 0 47px;
}
#access {
background: #fff; /* Show a solid color for older browsers */
background: -moz-linear-gradient(#fff, #fff);
background: -o-linear-gradient(#fff, #fff);
background: -webkit-gradient(linear, 0% 0%, 0% 100%, from(#fff), to(#fff)); /* older webkit syntax */
background: -webkit-linear-gradient(#fff, #fff);
-webkit-box-shadow: rgba(0, 0, 0, 0.4) 0px 0px 0px;
-moz-box-shadow: rgba(0, 0, 0, 0.4) 0px 0px 0px;
box-shadow: rgba(0, 0, 0, 0.4) 0px 0px 0px;
clear: both;
float:none;
text-align:center;
margin: 0 auto 0;
width: 950px;
text-transform:uppercase;
font-weight:bold;
display:block;
}
#access ul {
font-size: 10px;
list-style: none;
margin: 0 0 0 0;
padding-left: 0;
}
#access li {
float:left;
position: relative;
}
#access a {
color: #5288a9;
display: block;
line-height: 3.333em;
padding: 0 13px;
font-weight:900;
text-decoration: none;
}
#access ul ul {
-moz-box-shadow: 0 3px 3px rgba(0,0,0,0.2);
-webkit-box-shadow: 0 3px 3px rgba(0,0,0,0.2);
box-shadow: 0 3px 3px rgba(0,0,0,0.2);
background: rgba(255,255,255,0.9);
display: none;
float: none;
margin: 0 0 0 19px;
position: absolute;
top: 3.333em;
left: 0;
width: 169px;
z-index: 99999;
border-left:0px solid #5288a9;
}
#access ul ul ul {
background: rgba(255,255,255,0.9);
left: 100%;
top: 0;
border-left:2px solid #5288a9;
margin-left:0px;
}
#ie8 #access ul ul, #ie8 #access ul ul ul {-ms-filter: "progid:DXImageTransform.Microsoft.gradient(startColorstr=#CCFFFFFF, endColorstr=#CCFFFFFF)";}
#access ul ul a {
text-align:left;
background: transparent;
border-bottom: 1px dotted #ddd;
color: #5288a9;
font-size: 10px;
font-weight: bold;
height: auto;
line-height: 1.4em;
padding: 10px 10px 10px 6px;
width: 153px;
}
#access li:hover > a,
#access ul ul :hover > a,
#access a:focus {
background: #fff;
}
#access li:hover > a,
#access a:focus {
background: #fff; /* Show a solid color for older browsers */
background: -moz-linear-gradient(#fff, #fff);
background: -o-linear-gradient(#fff, #fff);
background: -webkit-gradient(linear, 0% 0%, 0% 100%, from(#fff), to(#fff)); /* Older webkit syntax */
background: -webkit-linear-gradient(#fff, #fff);
color: #373737;
}
#access ul li:hover > ul {
display: block;
}
#access .current-menu-item > a,
#access .current-menu-ancestor > a,
#access .current_page_item > a,
#access .current_page_ancestor > a {
font-weight: bold; color:#f88721;
}