How to fix this IE7-dropdown menu problem?

This is the CSS for the dropdown menu I create, the problem is that the menu disappears as soon as I hover the children items.

It gets fixed If I set Height:30px and line-height: 30px but I do not want to adjust height. I want it to auto adjust. I can't get it to work in IE7. This is my CSS

#menu {
    display: block;
    width: 1000px;
    height: 30px;
    background: url(../images/modern/menu.png) no-repeat;
    margin: 10px 0 0 0;
    position: relative;
    z-index: 10;
}

#menu ul {
    float: left;
    margin: 0 0 0 5px;
    display: inline;
    width: 795px;
}

#menu ul li {
    position: relative;
    float: left;
    display: block;
    position: relative;
}

#menu ul li a {
    float: left;
    display:开发者_高级运维 block;
    color: #fff;
    font-weight: bold;
    padding: 9px 10px 9px 10px;
    background: url(../images/modern/menu_l.png) no-repeat right;
}

/* sub menu style */
#menu ul ul {
    padding:0;margin:0;border:none;
    float: none;
    display: none;
    position: absolute;
    z-index: 10;
    width: 190px;
    top: 29px;
    left: 0;
}
#menu ul ul ul {
    top: 0;
    left: 190px;
}

#menu ul ul li {
    float: none;
    display: block;
    position: relative;
}

#menu ul ul li a {
    padding:0;margin:0;border:none;
    float: none;
    display: block;
    font-weight: bold;
    position: static;
    background: none;
    color: #fff;
    padding: 6px 10px 6px 10px;
    background: #333;
    border-bottom: 1px solid #444;
}

This fixes it but I really do not want to set height for child item:

#menu ul ul li a {
    padding:0;margin:0;border:none;
    float: none;
    display: block;
    font-weight: bold;
    position: static;
    background: none;
    color: #fff;
    padding: 6px 10px 6px 10px;
    background: #333;
    border-bottom: 1px solid #444;
    height: 30px;
    line-height: 30px;
}

Try zoom:1; to the thing you applied height:30px; to.