I’ve found a reference to it and a possible solution at http://www.highdots.com/forums/javascript/dropdown-menu-stays-open-ie7-262928.html
Here is the main part:
<blockquote>Thanks for your information. It seemed a queer bug in IE7.
I have a “solution” now, it was detected by someone at alt.html. You can
read the thread there (similar subject name and recent). Basically it
was reaction by IE7 to a lack of a change in styling between the state
of a link and its hover, IE7 seems to need various differences. For
example commenting out
dropDownNav, .dropDownNav ul {
padding: 0;
margin: 0;
color: #00c;
background: #ffc;
/* list-style-type: none; */
line-height: 1.8;
}
stops the queer phenomenon. Odd bug but have we not come to expect such
from IE?</blockquote>
Its a starting point if not a fix. 🙂